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)

app/plugin_hooks_test.go

@@ -181,7 +181,7 @@ func TestHookMessageWillBePosted(t *testing.T) {
 		require.Nil(t, err)
 
 		assert.Equal(t, "message", post.Message)
-		retrievedPost, errSingle := th.App.Srv().Store.Post().GetSingle(post.Id)
+		retrievedPost, errSingle := th.App.Srv().Store.Post().GetSingle(post.Id, false)
 		require.NoError(t, errSingle)
 		assert.Equal(t, "message", retrievedPost.Message)
 	})
@@ -225,7 +225,7 @@ func TestHookMessageWillBePosted(t *testing.T) {
 		require.Nil(t, err)
 
 		assert.Equal(t, "message_fromplugin", post.Message)
-		retrievedPost, errSingle := th.App.Srv().Store.Post().GetSingle(post.Id)
+		retrievedPost, errSingle := th.App.Srv().Store.Post().GetSingle(post.Id, false)
 		require.NoError(t, errSingle)
 		assert.Equal(t, "message_fromplugin", retrievedPost.Message)
 	})