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>

api/v4/source/definitions.yaml

@@ -3485,6 +3485,39 @@ components:
         remote_id:
           description: Id of the remote cluster where the shared channel is homed
           type: string
+    RemoteCluster:
+      type: object
+      properties:
+        remote_id:
+          type: string
+        remote_team_id:
+          type: string
+        name:
+          type: string
+        display_name:
+          type: string
+        site_url:
+          description: URL of the remote cluster
+          type: string
+        create_at:
+          description: Time in milliseconds that the remote cluster was created
+          type: integer
+        last_ping_at:
+          description: Time in milliseconds when the last ping to the remote cluster was run
+          type: integer
+        token:
+          type: string
+        remote_token:
+          type: string
+        topics:
+          type: string
+        creator_id:
+          type: string
+        plugin_id:
+          type: string
+        options:
+          description: A bitmask with a set of option flags
+          type: integer
     RemoteClusterInfo:
       type: object
       properties: