Add StagingController

we created this method to not repeat and have different methods to do the same.

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

@@ -0,0 +1,26 @@
+module Staging
+  class StagingController < ApplicationController
+    private
+
+    def set_project
+      @project = Project.get_by_name(params[:staging_workflow_project])
+    rescue Project::UnknownObjectError
+      render_error(
+        status: 404,
+        errorcode: 'not_found',
+        message: "Project '#{params[:staging_workflow_project]}' not found."
+      )
+    end
+
+    def set_staging_workflow
+      @staging_workflow = @project.staging
+      return if @staging_workflow
+
+      render_error(
+        status: 404,
+        errorcode: 'not_found',
+        message: "Project #{@project} doesn't have an asociated Staging Workflow"
+      )
+    end
+  end
+end