docs: release notes for 1.5 (#19530)

* docs: release notes for 1.5

* rephrase and remove secret key from 1.4

* address review comments

(cherry picked from commit 1c1beb6)

RELEASING/README.md

@@ -30,6 +30,7 @@ partaking in the process should join the channel.
 
 ## Release notes for recent releases
 
+- [1.5](release-notes-1-5/README.md)
 - [1.4](release-notes-1-4/README.md)
 - [1.3](release-notes-1-3/README.md)
 - [1.2](release-notes-1-2/README.md)

RELEASING/release-notes-1-5/README.md

@@ -0,0 +1,142 @@
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+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
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+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+# Release Notes for Superset 1.5
+
+Superset 1.5 focuses on polishing the dashboard native filters experience, while
+improving performance and stability. Superset 1.5 is likely the last minor release of
+version 1 of Superset, and will be succeeded by Superset 2.0. The 1.5 branch
+introduces the notion of a Long Term Support (LTS) version of Superset, and will
+receive security and other critical fixes even after Superset 2.x is released.
+Therefore, users will have the choice of staying on the 1.5 branch or upgrading to 2.x
+when available.
+
+- [**User Experience**](#user-facing-features)
+- [**Feature flags**](#feature-flags)
+- [**Database Experience**](#database-experience)
+- [**Breaking Changes and Full Changelog**](#breaking-changes-and-full-changelog)
+
+## User Facing Features
+
+- Complex dashboards with lots of native filters and charts will render considerably
+  faster. See the videos that shows the rendering time of a complex dashboard go from
+  11 to 3 seconds: [#19064](https://github.com/apache/superset/pull/19064). In
+  addition, applying filters and switching tabs is also much smoother.
+- The Native Filter Bar has been redesigned, along with moving the "Apply" and
+  "Clear all" buttons to the bottom:
+
+![Filter bar](media/filter_bar.png)
+
+- Native filters can now be made dependent on multiple filters. This makes it possible
+  to restrict the available values in a filter based on the selection of other filters.
+
+![Dependent filters](media/dependent_filters.png)
+
+- In addition to being able to write Custom SQL for adhoc metrics and filters, the
+  column control now also features a Custom SQL tab. This makes it possible to write
+  custom expressions directly in charts without adding them to the dataset as saved
+  expressions.
+
+![Adhoc columns](media/adhoc_columns.png)
+
+- A new `SupersetMetastoreCache` has been added which makes it possible to cache data
+  in the Superset Metastore without the need for running a dedicated cache like Redis
+  or Memcached. The new cache will be used by default for required caches, but can also
+  be used for caching chart or other data. See the
+  [documentation](https://superset.apache.org/docs/installation/cache#caching) for
+  details on using the new cache.
+- Previously it was possible for Dashboards with lots of filters to cause an error.
+  A similar issue existed on Explore. Now Superset stores Dashboard and Explore state
+  in the cache (as opposed to the URL), eliminating the infamous
+  [Long URL Problem](https://github.com/apache/superset/issues/17086).
+- Previously permanent links to Dashboard and Explore pages were in fact shortened URLS
+  that relied on state being stored in the URL (see Long URL Problem above). In
+  addition, the links used numerical ids and didn't check user permissions making it
+  easy to iterate through links that were stored in the metastore. Now permanent links
+  state is stored as JSON objects in the metastore, making it possible to store
+  arbitrarily large Dashboard and Explore state in permalinks. In addition, the ids
+  are encoded using [`hashids`](https://hashids.org/) and check permissions, making
+  permalink state more secure.
+
+![Dashboard permalink](media/permalink.png)
+
+## Feature flags
+
+- A new feature flag `GENERIC_CHART_AXES` has been added that makes it possible to
+  use a non-temporal x-axis on the ECharts Timeseries chart
+  ([#17917](https://github.com/apache/superset/pull/17917)). When enabled, a new
+  control "X Axis" is added to the control panel of ECharts line, area, bar, step and
+  scatter charts, which makes it possible to use categorical or numerical x-axes on
+  those charts.
+
+![Categorical line chart](media/categorical_line.png)
+
+## Database Experience
+
+- DuckDB: Add support for database:
+  [#19317](https://github.com/apache/superset/pull/19317)
+
+- Kusto: Add support for Azure Data Explorer (Kusto):
+  [#17898](https://github.com/apache/superset/pull/17898)
+
+- Trino: Add server cert support and new auth methods:
+  [#17593](https://github.com/apache/superset/pull/17593) and
+  [#16346](https://github.com/apache/superset/pull/16346)
+
+- Microsoft SQL Server (MSSQL): support using CTEs in virtual tables:
+  [#18567](https://github.com/apache/superset/pull/18567)
+
+- Teradata and MSSQL: add support for TOP limit syntax:
+  [#18746](https://github.com/apache/superset/pull/18746) and
+  [#18240](https://github.com/apache/superset/pull/18240)
+
+- Apache Drill: User impersonation using `drill+sadrill`:
+  [#19252](https://github.com/apache/superset/pull/19252)
+
+## Developer Experience
+
+- `superset-ui` has now been integrated into the Superset codebase as per
+  [SIP-58](https://github.com/apache/superset/issues/13013) dubbed "Monorepo". This
+  makes development of plugins that ship with Superset considerably simpler. In
+  addition, it makes it possible to align `superset-ui` releases with official Superset
+  releases.
+
+## Breaking Changes and Full Changelog
+
+**Breaking Changes**
+
+- Bump `mysqlclient` from v1 to v2:
+  [#17556](https://github.com/apache/superset/pull/17556)
+- Single and double quotes will no longer be removed from filter values:
+  [#17881](https://github.com/apache/superset/pull/17881)
+- Previously `QUERY_COST_FORMATTERS_BY_ENGINE`, `SQL_VALIDATORS_BY_ENGINE` and
+  `SCHEDULED_QUERIES` were expected to be defined in the feature flag dictionary in
+  the `config.py` file. These should now be defined as a top-level config, with the
+  feature flag dictionary being reserved for boolean only values:
+  [#15254](https://github.com/apache/superset/pull/15254)
+- All Superset CLI commands (init, load_examples and etc) require setting the
+  `FLASK_APP` environment variable (which is set by default when `.flaskenv` is loaded):
+  [#17539](https://github.com/apache/superset/pull/17539)
+
+**Changelog**
+
+To see the complete changelog in this release, head to
+[CHANGELOG.MD](https://github.com/apache/superset/blob/1.5/CHANGELOG.md).
+As mentioned earlier, this release has a MASSIVE amount of bug fixes. The full
+changelog lists all of them!