MM-27493 Shared channels (MVP) (#17301)

Remote Cluster Service
- provides ability for multiple Mattermost cluster instances to create a trusted connection with each other and exchange messages
- trusted connections are managed via slash commands (for now)
- facilitates features requiring inter-cluster communication, such as Shared Channels
Shared Channels Service
- provides ability to shared channels between one or more Mattermost cluster instances (using trusted connection)
- sharing/unsharing of channels is managed via slash commands (for now)

store/storetest/thread_store.go

@@ -145,7 +145,7 @@ func testThreadStorePopulation(t *testing.T, ss store.Store) {
 		thread1, err := ss.Thread().Get(newPosts[0].RootId)
 		require.NoError(t, err)
 
-		rrootPost, err := ss.Post().GetSingle(rootPost.Id)
+		rrootPost, err := ss.Post().GetSingle(rootPost.Id, false)
 		require.NoError(t, err)
 		require.Equal(t, rrootPost.UpdateAt, rootPost.UpdateAt)
 
@@ -164,7 +164,7 @@ func testThreadStorePopulation(t *testing.T, ss store.Store) {
 		_, _, err = ss.Post().SaveMultiple([]*model.Post{&replyPost2, &replyPost3})
 		require.NoError(t, err)
 
-		rrootPost2, err := ss.Post().GetSingle(rootPost.Id)
+		rrootPost2, err := ss.Post().GetSingle(rootPost.Id, false)
 		require.NoError(t, err)
 		require.Greater(t, rrootPost2.UpdateAt, rrootPost.UpdateAt)