Implements the changes in the API made in readthedocs/readthedocs.org#11205. We need to merge that PR and deploy addons together with the changes in this PR.

In this PR there are mainly no changes in the logic. The most important thing to mention here is that we are standardizing the usage of the API response and pinning to v1 now (we were using v0-alpha). This means:

• we will be exposing the v1 to users via the js custom event (see API: use <meta> to define supported API version and trigger CustomEvent #64)
• we are using standard/shared APIv3 serializers for resources for this /addons/ endpoint
• any breaking change we have to do in the future it will increase the API response version

I'm not sure there are too much to review here, but I'd appreciate at least a quick look at these changes. I'm happy to answer some questions you may have here or on the underlying PR about the API response changes.

Related:

• Closes Notification: handle stable/latest aliases #132
• Unblocks Notifications: respect project.versioning_scheme for links #265
• Unblocks theme integration (our theme and CPython's one)
• Requires APIv3: add more generic fields readthedocs.org#11205