Add check for previously existing staging workflow

Verification of a previously existing staging workflow for a project was missing
on staging workflow creation.

Fixes #8714.

Co-authored-by: David Kang <dkang@suse.com>
Co-authored-by: Saray Cabrera Padrón <scabrerapadron@suse.de>

src/api/app/controllers/staging/workflows_controller.rb

@@ -1,6 +1,7 @@
 class Staging::WorkflowsController < Staging::StagingController
   before_action :require_login
   before_action :set_project
+  before_action :check_staging_workflow, only: :create
   before_action :set_staging_workflow, only: [:update, :destroy]
   after_action :verify_authorized
 
@@ -50,6 +51,16 @@ def update
 
   private
 
+  def check_staging_workflow
+    return unless @project.staging
+
+    render_error(
+      status: 400,
+      errorcode: 'staging_workflow_exists',
+      message: "Project #{@project} already has an associated Staging Workflow with id: #{@project.staging.id}"
+    )
+  end
+
   def xml_hash
     Xmlhash.parse(request.body.read) || {}
   end