Put .gitlab-ci.yml linting in IDE behind a feature flag

This is needed so that we turn on the feature flag only for GitLab.com
and turn it off for self-managed by default. Since this feature sends a request to
a third party URL, some self-managed hosts may not like it much.

app/assets/javascripts/ide/lib/editor.js

@@ -45,7 +45,10 @@ export default class Editor {
 
     setupThemes();
     registerLanguages(...languages);
-    registerSchemas(...schemas);
+
+    if (gon.features?.schemaLinting) {
+      registerSchemas(...schemas);
+    }
 
     this.debouncedUpdate = debounce(() => {
       this.updateDimensions();

app/controllers/ide_controller.rb

@@ -8,6 +8,7 @@ class IdeController < ApplicationController
 
   before_action do
     push_frontend_feature_flag(:build_service_proxy)
+    push_frontend_feature_flag(:schema_linting)
   end
 
   def index

spec/frontend/ide/lib/editor_spec.js

@@ -200,6 +200,20 @@ describe('Multi-file editor library', () => {
   });
 
   describe('schemas', () => {
+    let originalGon;
+
+    beforeEach(() => {
+      originalGon = window.gon;
+      window.gon = { features: { schemaLinting: true } };
+
+      delete Editor.editorInstance;
+      instance = Editor.create();
+    });
+
+    afterEach(() => {
+      window.gon = originalGon;
+    });
+
     it('registers custom schemas defined with Monaco', () => {
       expect(monacoLanguages.yaml.yamlDefaults.diagnosticsOptions).toMatchObject({
         schemas: [{ fileMatch: ['*.gitlab-ci.yml'] }],