Add time grain blacklist and addons to config.py (apache#5380)

* Add interim grains

* Refactor and add blacklist

* Change PT30M to PT0.5H

* Linting

* Linting

* Add time grain addons to config.py and refactor engine spec logic

* Remove redundant import and clean up config.py

* Fix bad rebase

* Implement changes proposed by @betodealmeida

* Revert removal of name from Grain

* Linting

superset/config.py

@@ -200,6 +200,30 @@
     'encoding': 'utf-8',
 }
 
+# ---------------------------------------------------
+# Time grain configurations
+# ---------------------------------------------------
+# List of time grains to disable in the application (see list of builtin
+# time grains in superset/db_engine_specs.builtin_time_grains).
+# For example: to disable 1 second time grain:
+# TIME_GRAIN_BLACKLIST = ['PT1S']
+TIME_GRAIN_BLACKLIST = []
+
+# Additional time grains to be supported using similar definitions as in
+# superset/db_engine_specs.builtin_time_grains.
+# For example: To add a new 2 second time grain:
+# TIME_GRAIN_ADDONS = {'PT2S': '2 second'}
+TIME_GRAIN_ADDONS = {}
+
+# Implementation of additional time grains per engine.
+# For example: To implement 2 second time grain on clickhouse engine:
+# TIME_GRAIN_ADDON_FUNCTIONS = {
+#     'clickhouse': {
+#         'PT2S': 'toDateTime(intDiv(toUInt32(toDateTime({col})), 2)*2)'
+#     }
+# }
+TIME_GRAIN_ADDON_FUNCTIONS = {}
+
 # ---------------------------------------------------
 # List of viz_types not allowed in your environment
 # For example: Blacklist pivot table and treemap: