Adds logical deletes to shared channel remotes and remote clusters (#28159)

* Adds logical deletes to shared channel remotes and remote clusters

Instead of physically deleting the shared channel remote and remote
clusters records when a channel is unshared, a remote uninvited or a
remote cluster is deleted, now those have a logical `DeleteAt` field
that is set.

This allows us to safely restore shared channels between two remote
clusters (as of now resetting the cursor without backfilling their
contents) and to know which connections were established in the past
and now are severed.

* Delete the index in remoteclusters before adding the new column

* Fix bad error check

api/v4/source/definitions.yaml

@@ -3505,6 +3505,9 @@ components:
         create_at:
           description: Time in milliseconds that the remote cluster was created
           type: integer
+        delete_at:
+          description: Time in milliseconds that the remote cluster record was deleted
+          type: integer
         last_ping_at:
           description: Time in milliseconds when the last ping to the remote cluster was run
           type: integer
@@ -3553,6 +3556,9 @@ components:
         update_at:
           description: Time in milliseconds that the shared channel remote record was last updated
           type: integer
+        delete_at:
+          description: Time in milliseconds that the shared chanenl remote record was deleted
+          type: integer
         is_invite_accepted:
           description: Indicates if the invite has been accepted by the remote
           type: boolean