Display pinned messages on a banner at the top of a room (#12917)

* Move pinned message hooks to a dedicated file

* Add a banner at the top of a room to display the pinned messages

* Put the pinning banner behind labs pinning labs flag

* Add redacted event support

* Handle UTD in pinning message banner

* Add tests for redaction

* Make all the banner clickable

* Add tests for PinnedMessageBanner.tsx

* Add e2e tests for the pinned message banner

* Review changes