docs(issue-search): Warn against enabling postgres only search (#54434)

We enabled this flag on the sentry org and it was causing us to not
correctly filter out unreleased issue platform issues. Luckily didn't
cause any customer production issues, but just warning future folks from
doing the same thing.

src/sentry/search/snuba/executors.py

@@ -787,6 +787,8 @@ class PostgresSnubaQueryExecutor(AbstractQueryExecutor):
         # are no other Snuba-based search predicates, we can simply
         # return the results from Postgres.
         if (
+            # XXX: Don't enable this for now, it doesn't properly respect issue platform rules for hiding issue types.
+            # We'll need to consolidate where we apply the type filters if we do want this.
             allow_postgres_only_search
             and cursor is None
             and sort_by == "date"