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)

api4/post_test.go

@@ -618,7 +618,7 @@ func TestCreatePostCheckOnlineStatus(t *testing.T) {
 				}
 			case <-timeout:
 				// We just skip the test instead of failing because waiting for more than 5 seconds
-				// to get a response does not make sense, and it will unncessarily slow down
+				// to get a response does not make sense, and it will unnecessarily slow down
 				// the tests further in an already congested CI environment.
 				t.Skip("timed out waiting for event")
 			}
@@ -2035,7 +2035,7 @@ func TestDeletePostMessage(t *testing.T) {
 					}
 				case <-timeout:
 					// We just skip the test instead of failing because waiting for more than 5 seconds
-					// to get a response does not make sense, and it will unncessarily slow down
+					// to get a response does not make sense, and it will unnecessarily slow down
 					// the tests further in an already congested CI environment.
 					t.Skip("timed out waiting for event")
 				}