Addons: prepare Proxito and dashboard to enable them by default

Prepare Proxito's code and dashboard to enable addons by default starting on
October 7th, as planned:
https://about.readthedocs.com/blog/2024/07/addons-by-default/

Note this code is temporary and can be deployed _before_ reaching that
particular date. The idea is to remove this code once this behavior becomes the
default.

Related #11474

readthedocs/projects/forms.py

@@ -1,16 +1,19 @@
 """Project forms."""
 
+import datetime
 import json
 from random import choice
 from re import fullmatch
 from urllib.parse import urlparse
 
+import pytz
 from allauth.socialaccount.models import SocialAccount
 from django import forms
 from django.conf import settings
 from django.contrib.auth.models import User
 from django.db.models import Q
 from django.urls import reverse
+from django.utils import timezone
 from django.utils.translation import gettext_lazy as _
 
 from readthedocs.builds.constants import INTERNAL
@@ -662,14 +665,23 @@ class Meta:
 
     def __init__(self, *args, **kwargs):
         self.project = kwargs.pop("project", None)
+
+        tzinfo = pytz.timezone("America/Los_Angeles")
+        addons_enabled_by_default = timezone.now() > datetime.datetime(
+            2024, 10, 7, 0, 0, 0, tzinfo=tzinfo
+        )
+
         addons, created = AddonsConfig.objects.get_or_create(project=self.project)
         if created:
-            addons.enabled = False
+            addons.enabled = addons_enabled_by_default
             addons.save()
 
         kwargs["instance"] = addons
         super().__init__(*args, **kwargs)
 
+        if addons_enabled_by_default:
+            self.fields.pop("enabled")
+
     def clean(self):
         if (
             self.cleaned_data["flyout_sorting"] == ADDONS_FLYOUT_SORTING_CUSTOM_PATTERN

readthedocs/proxito/middleware.py

@@ -31,7 +31,7 @@
     unresolver,
 )
 from readthedocs.core.utils import get_cache_tag
-from readthedocs.projects.models import Project
+from readthedocs.projects.models import Feature, Project
 from readthedocs.proxito.cache import add_cache_tags, cache_response, private_response
 from readthedocs.proxito.redirects import redirect_to_https
 
@@ -289,11 +289,19 @@ def add_hosting_integrations_headers(self, request, response):
         version_slug = getattr(request, "path_version_slug", "")
 
         if project_slug:
+            # TODO: update this code once DISABLE_SPHINX_MANIPULATION and addons becomes the default
+            # https://about.readthedocs.com/blog/2024/07/addons-by-default/
+            disable_sphinx_manipulation_enabled = Feature.objects.filter(
+                feature_id=Feature.DISABLE_SPHINX_MANIPULATION,
+                projects__slug=Project.objects.filter(slug=project_slug).first(),
+            ).exists()
+
             force_addons = Project.objects.filter(
                 slug=project_slug,
                 addons__enabled=True,
             ).exists()
-            if force_addons:
+
+            if force_addons or disable_sphinx_manipulation_enabled:
                 response["X-RTD-Force-Addons"] = "true"
                 return