[Comments] Update Comments Action visibility when the group is shared/unshared

Observe the TabGroupSyncService and update Comments Action and Side
Panel when the current active tab group is updated. This handles when
the active tab is in a group that becomes shared or unshared.

Fixed: 433773768
Change-Id: I9546804f6dcf5a462ca09dc5631945322c1eac4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6812943
Reviewed-by: David Pennington <dpenning@chromium.org>
Commit-Queue: Mickey Burks <mickeyburks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1497174}