chore(config): Deprecating Domain Sharding (#31894)

UPDATING.md

@@ -23,6 +23,7 @@ This file documents any backwards-incompatible changes in Superset and
 assists people when migrating to a new version.
 
 ## Next
+- [31894](https://github.com/apache/superset/pull/31894) Domain sharding is deprecated in favor of HTTP2. The `SUPERSET_WEBSERVER_DOMAINS` configuration will be removed in the next major version (6.0)
 - [31774](https://github.com/apache/superset/pull/31774): Fixes the spelling of the `USE-ANALAGOUS-COLORS` feature flag. Please update any scripts/configuration item to use the new/corrected `USE-ANALOGOUS-COLORS` flag spelling.
 - [31582](https://github.com/apache/superset/pull/31582) Removed the legacy Area, Bar, Event Flow, Heatmap, Histogram, Line, Sankey, and Sankey Loop charts. They were all automatically migrated to their ECharts counterparts with the exception of the Event Flow and Sankey Loop charts which were removed as they were not actively maintained and not widely used. If you were using the Event Flow or Sankey Loop charts, you will need to find an alternative solution.
 - [31198](https://github.com/apache/superset/pull/31198) Disallows by default the use of the following ClickHouse functions: "version", "currentDatabase", "hostName".

docs/docs/configuration/networking-settings.mdx

@@ -108,6 +108,10 @@ running a custom auth postback endpoint), you can add the endpoints to `WTF_CSRF
 
 ## Domain Sharding
 
+:::note
+Domain Sharding is deprecated as of Superset 5.0.0, and will be removed in Superset 6.0.0. Please Enable HTTP2 to keep more open connections per domain.
+:::
+
 Chrome allows up to 6 open connections per domain at a time. When there are more than 6 slices in
 dashboard, a lot of time fetch requests are queued up and wait for next available socket.
 [PR 5039](https://github.com/apache/superset/pull/5039) adds domain sharding to Superset,

superset/config.py

@@ -834,10 +834,11 @@ class D3TimeFormat(TypedDict, total=False):
 
 # Chrome allows up to 6 open connections per domain at a time. When there are more
 # than 6 slices in dashboard, a lot of time fetch requests are queued up and wait for
-# next available socket. PR #5039 is trying to allow domain sharding for Superset,
-# and this feature will be enabled by configuration only (by default Superset
-# doesn't allow cross-domain request).
-SUPERSET_WEBSERVER_DOMAINS = None
+# next available socket. PR #5039 added domain sharding for Superset,
+# and this feature can be enabled by configuration only (by default Superset
+# doesn't allow cross-domain request). This feature is deprecated, annd will be removed
+# in the next major version of Superset, as enabling HTTP2 will serve the same goals.
+SUPERSET_WEBSERVER_DOMAINS = None  # deprecated
 
 # Allowed format types for upload on Database view
 EXCEL_EXTENSIONS = {"xlsx", "xls"}