Addons: expose readthedocs.resolver.filename in the API response

This is required to be able to dynamically update the URLs from the versions in
the flyout when the page is changed using `history` object (without reloading /
SPA) as Docusaurus does.

In that scenario we cannot use the HTML META tag because it was injected with
the old value by CF Worker. Note that the CF Worker is not run after the initial
request on SPA.

The addons frontend will use this attribute to update those URLs accordingly
when the URL changes.

Required by:
* readthedocs/addons#504

readthedocs/proxito/views/hosting.py

@@ -7,6 +7,8 @@
 from django.contrib.auth.models import AnonymousUser
 from django.http import Http404, JsonResponse
 from django.shortcuts import get_object_or_404
+from django.utils.encoding import iri_to_uri
+from django.utils.html import escape
 from rest_framework import permissions
 from rest_framework.renderers import JSONRenderer
 from rest_framework.views import APIView
@@ -452,6 +454,9 @@ def _v1(self, project, version, build, filename, url, request):
                 "analytics": {
                     "code": settings.GLOBAL_ANALYTICS_CODE,
                 },
+                "resolver": {
+                    "filename": escape(iri_to_uri(filename)),
+                },
             },
             # TODO: the ``features`` is not polished and we expect to change drastically.
             # Mainly, all the fields including a Project, Version or Build will use the exact same