Add test for basic remote replication

Here's what I was proposing in our chat: #2927248: Make upstream plugins non-configurable by default and improve their integration with the Workspace entity , and why I think the 'remote' annotation key is quite useful.

Given the issue above, this test needs to go through the entire flow:

- go to the workspace add form
- select the test remote upstream plugin
- check that the configuration form appears
- fill in values for the endpoint URL
- check that the values were correctly saved in the database by instantiating the plugin with $upstream = $workspace->getUpstreamPlugin() and looking at $upstream->getConfiguration()

1. +++ b/tests/modules/workspace_remote_test/src/Plugin/rest/resource/ReplicationResource.php
   @@ -0,0 +1,115 @@
   + *     "create" = "/admin/config/workflow/workspace/{workspace}/replication"
   ...
   +  public function post($workspace_id, $revisions) {
   

   This does not match.

   If the parameter would be WorkspaceInterface $workspace, then it'd automatically receive the entity.

2. +++ b/tests/modules/workspace_remote_test/src/Plugin/rest/resource/ReplicationResource.php
   @@ -0,0 +1,115 @@
   +    $this->serializer = $serializer;
   ...
   +        $entity = $this->serializer->deserialize(json_encode($revision), $class, 'json');
   

   All of this should not be necessary, \Drupal\rest\RequestHandler::handle() takes care of this.

3. +++ b/tests/modules/workspace_remote_test/src/Plugin/rest/resource/ReplicationResource.php
   @@ -0,0 +1,115 @@
   +    return new ResourceResponse(TRUE);
   

   This … does not make sense. See \Drupal\rest\Plugin\rest\resource\EntityResource::post(). It should return a ModifiedResourceResponse containing the created data, or at least links to the created data.

Fix component following module rename.

Remote replication is not in the scope of the core Workspaces module anymore, so moving back to the contrib queue for now.