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/platform/services/remotecluster/mocks_test.go

@@ -52,7 +52,7 @@ func (ms *mockServer) GetStore() store.Store {
 
 	remoteClusterStoreMock := &mocks.RemoteClusterStore{}
 	remoteClusterStoreMock.On("GetByTopic", "share").Return(ms.remotes, nil)
-	remoteClusterStoreMock.On("GetAll", anyQueryFilter).Return(ms.remotes, nil)
+	remoteClusterStoreMock.On("GetAll", 0, 999999, anyQueryFilter).Return(ms.remotes, nil)
 	remoteClusterStoreMock.On("SetLastPingAt", anyId).Return(nil)
 
 	userStoreMock := &mocks.UserStore{}