Get standard context data from backend

This creates a bridge between backend and frontend
to load snowplow related data.

app/assets/javascripts/tracking.js

 import { omitBy, isUndefined } from 'lodash';
 
+const standardContext = { ...window.gl?.snowplowStandardContext };
+
 export const STANDARD_CONTEXT = {
-  schema: 'iglu:com.gitlab/gitlab_standard/jsonschema/1-0-3',
+  schema: standardContext.schema,
   data: {
-    environment: process.env.NODE_ENV,
+    ...(standardContext.data || {}),
     source: 'gitlab-javascript',
   },
 };

app/views/layouts/_snowplow.html.haml

@@ -8,3 +8,6 @@
     n.src=w;g.parentNode.insertBefore(n,g)}}(window,document,"script","#{asset_url('snowplow/sp.js')}","snowplow"));
 
     window.snowplowOptions = #{Gitlab::Tracking.snowplow_options(@group).to_json}
+
+    gl = window.gl || {};
+    gl.snowplowStandardContext = #{Gitlab::Tracking::StandardContext.new.to_context.to_json.to_json}

spec/frontend/tracking_spec.js

@@ -78,6 +78,34 @@ describe('Tracking', () => {
       navigator.msDoNotTrack = undefined;
     });
 
+    describe('builds the standard context', () => {
+      let standardContext;
+
+      beforeAll(async () => {
+        window.gl = window.gl || {};
+        window.gl.snowplowStandardContext = {
+          schema: 'iglu:com.gitlab/gitlab_standard',
+          data: {
+            environment: 'testing',
+            source: 'unknown',
+          },
+        };
+
+        jest.resetModules();
+
+        ({ STANDARD_CONTEXT: standardContext } = await import('~/tracking'));
+      });
+
+      it('uses server data', () => {
+        expect(standardContext.schema).toBe('iglu:com.gitlab/gitlab_standard');
+        expect(standardContext.data.environment).toBe('testing');
+      });
+
+      it('overrides schema source', () => {
+        expect(standardContext.data.source).toBe('gitlab-javascript');
+      });
+    });
+
     it('tracks to snowplow (our current tracking system)', () => {
       Tracking.event('_category_', '_eventName_', { label: '_label_' });