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/invitation.go

@@ -12,7 +12,7 @@ import (
 )
 
 // AcceptInvitation is called when accepting an invitation to connect with a remote cluster.
-func (rcs *Service) AcceptInvitation(invite *model.RemoteClusterInvite, name string, displayName, creatorId string, teamId string, siteURL string) (*model.RemoteCluster, error) {
+func (rcs *Service) AcceptInvitation(invite *model.RemoteClusterInvite, name string, displayName, creatorId string, siteURL string) (*model.RemoteCluster, error) {
 	rc := &model.RemoteCluster{
 		RemoteId:    invite.RemoteId,
 		Name:        name,
@@ -29,7 +29,7 @@ func (rcs *Service) AcceptInvitation(invite *model.RemoteClusterInvite, name str
 	}
 
 	// confirm the invitation with the originating site
-	frame, err := makeConfirmFrame(rcSaved, teamId, siteURL)
+	frame, err := makeConfirmFrame(rcSaved, siteURL)
 	if err != nil {
 		return nil, err
 	}
@@ -60,7 +60,7 @@ func (rcs *Service) AcceptInvitation(invite *model.RemoteClusterInvite, name str
 	return rcSaved, nil
 }
 
-func makeConfirmFrame(rc *model.RemoteCluster, teamId string, siteURL string) (*model.RemoteClusterFrame, error) {
+func makeConfirmFrame(rc *model.RemoteCluster, siteURL string) (*model.RemoteClusterFrame, error) {
 	confirm := model.RemoteClusterInvite{
 		RemoteId: rc.RemoteId,
 		SiteURL:  siteURL,