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/store.go

@@ -533,7 +533,7 @@ type RemoteClusterStore interface {
 	Delete(remoteClusterId string) (bool, error)
 	Get(remoteClusterId string) (*model.RemoteCluster, error)
 	GetByPluginID(pluginID string) (*model.RemoteCluster, error)
-	GetAll(filter model.RemoteClusterQueryFilter) ([]*model.RemoteCluster, error)
+	GetAll(offset, limit int, filter model.RemoteClusterQueryFilter) ([]*model.RemoteCluster, error)
 	UpdateTopics(remoteClusterId string, topics string) (*model.RemoteCluster, error)
 	SetLastPingAt(remoteClusterId string) error
 }