Proxito: inject hosting integration header for build.commands

Versions using `build.commands` will start using the new Read the Docs
JavaScript client.

This is still under beta testing, but we want to move forward slowly and start
exposing these features to projects that don't have access currently.

Related readthedocs/addons#26

Author: humitos

readthedocs/proxito/middleware.py

@@ -281,11 +281,18 @@ def process_request(self, request):  # noqa
 
     def add_hosting_integrations_headers(self, request, response):
         project_slug = getattr(request, "path_project_slug", "")
+        version_slug = getattr(request, "path_version_slug", "")
+
         if project_slug:
             project = Project.objects.get(slug=project_slug)
             if project.has_feature(Feature.HOSTING_INTEGRATIONS):
                 response["X-RTD-Hosting-Integrations"] = "true"
 
+            # Inject the new integrations for versions using `build.commands`
+            version = project.versions.get(slug=version_slug)
+            if version.config.get("build", {}).get("commands", {}) != []:
+                response["X-RTD-Hosting-Integrations"] = "true"
+
     def process_response(self, request, response):  # noqa
         self.add_proxito_headers(request, response)
         self.add_cache_headers(request, response)