docs: Fix grammar of mat view WITH options

Fixes two issues:
- It looked as if `WITH ()` would be possible.
- It looked as if `ASSERT NOT NULL` and `RETAIN HISTORY` can come
  only in this order, but actually `ASSERT NOT NULL` can be specified
  also after `RETAIN HISTORY` (even both before and after).

Note that the new diagram is also not perfect, because now it looks as
if `RETAIN HISTORY` could be specified more than once. I think we have
to accept this, because it seems impossible to exactly specify using
BNF that these options can be specified in any order, and `ASSERT NOT
NULL` can be specified any number of times, but `RETAIN HISTORY` can
only be specified once.

Also, the new layout seems cleaner overall, especially when I add
REFRESH soon.

Note that I did not add the optional `=` for `ASSERT NOT NULL`. Started
a discussion on this here:
https://materializeinc.slack.com/archives/C063H5S7NKE/p1716888019218749

Plus the commit removes a stale PrPr notice fragment for
ASSERT NOT NULL.

doc/user/content/sql/create-materialized-view.md

@@ -23,6 +23,10 @@ resources used for view maintenance from the resources used for query serving.
 
 {{< diagram "with-options-materialized-view.svg" >}}
 
+### `with_option`
+
+{{< diagram "with-option-materialized-view.svg" >}}
+
 Field | Use
 ------|-----
 **OR REPLACE** | If a materialized view exists with the same name, replace it with the view defined in this statement. You cannot replace views that other views or sinks depend on, nor can you replace a non-view object with a view.
@@ -31,7 +35,7 @@ _view&lowbar;name_ | A name for the materialized view.
 **(** _col_ident_... **)** | Rename the `SELECT` statement's columns to the list of identifiers, both of which must be the same length. Note that this is required for statements that return multiple columns with the same identifier.
 _cluster&lowbar;name_ | The cluster to maintain this materialized view. If not specified, defaults to the active cluster.
 _select&lowbar;stmt_ | The [`SELECT` statement](../select) whose results you want to maintain incrementally updated.
-**(** **ASSERT NOT NULL** _col_ident_... **)** | This option has known performance or stability issues and is under active development.* A list of columns for which to create [non-null assertions](#non-null-assertions).
+**(** **ASSERT NOT NULL** _col_ident_... **)** | A list of columns for which to create [non-null assertions](#non-null-assertions).
 _retention_period_ | ***Private preview.** This option has known performance or stability issues and is under active development.* Duration for which Materialize retains historical data for performing [time travel queries](/transform-data/patterns/time-travel-queries). Accepts positive [interval](https://materialize.com/docs/sql/types/interval/) values (e.g. `'1hr'`). Default: `1s`.
 
 ## Details

doc/user/sql-grammar/sql-grammar.bnf

@@ -622,7 +622,10 @@ with_options_aws ::= 'WITH' '('
 with_options_aws_static ::=
   'access_key_id' '=' val ',' 'secret_access_key' '=' val ( ',' 'token' '=' val )?
 with_options_materialized_view ::=
-  ('WITH' '(' ( 'ASSERT NOT NULL' col_ident ( ',' 'ASSERT NOT NULL' col_ident )* )?
-    ( 'RETAIN HISTORY' '='? 'FOR' retention_period )?
-  ')')
+  ('WITH' '(' with_option ( ',' with_option )* ')')?
+with_option_materialized_view ::=
+  (
+    ( 'ASSERT NOT NULL' col_ident )
+    | ( 'RETAIN HISTORY' '='? 'FOR' retention_period )
+  )
 with_options_retain_history ::= ('WITH' '(' ('RETAIN HISTORY' '='? 'FOR' retention_period) ')')