Adds Remote Cluster related API endpoints (#27432)

* Adds Remote Cluster related API endpoints

New endpoints for the following routes are added:

- Get Remote Clusters at `GET /api/v4/remotecluster`
- Create Remote Cluster at `POST /api/v4/remotecluster`
- Accept Remote Cluster invite at `POST
/api/v4/remotecluster/accept_invite`
- Generate Remote Cluster invite at `POST
/api/v4/remotecluster/{remote_id}/generate_invite`
- Get Remote Cluster at `GET /api/v4/remotecluster/{remote_id}`
- Patch Remote Cluster at `PATCH /api/v4/remotecluster/{remote_id}`
- Delete Remote Cluster at `DELETE /api/v4/remotecluster/{remote_id}`

These endpoints are planned to be used from the system console, and
gated through the `manage_secure_connections` permission.

* Update server/channels/api4/remote_cluster_test.go

Co-authored-by: Doug Lauder <wiggin77@warpmail.net>

* Fix AppError names

---------

Co-authored-by: Doug Lauder <wiggin77@warpmail.net>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/store/timerlayer/timerlayer.go

@@ -7065,10 +7065,10 @@ func (s *TimerLayerRemoteClusterStore) Get(remoteClusterId string) (*model.Remot
 	return result, err
 }
 
-func (s *TimerLayerRemoteClusterStore) GetAll(filter model.RemoteClusterQueryFilter) ([]*model.RemoteCluster, error) {
+func (s *TimerLayerRemoteClusterStore) GetAll(offset int, limit int, filter model.RemoteClusterQueryFilter) ([]*model.RemoteCluster, error) {
 	start := time.Now()
 
-	result, err := s.RemoteClusterStore.GetAll(filter)
+	result, err := s.RemoteClusterStore.GetAll(offset, limit, filter)
 
 	elapsed := float64(time.Since(start)) / float64(time.Second)
 	if s.Root.Metrics != nil {