Addons: small improvements and privacy considerations

[stsewd]

• We had a special case in a permissions class, I moved this into the view itself.
• We are allowing some requests to not have a version, so our normal permission check doesn't work in this case. In case that we don't have a version, we just check for the project permission.
• If we have a version, we are attaching its latest build, this code was duplicated, and wasn't taking into considerations permissions. In case of temporal sharing tokens, they don't have access to builds.
• Translations now take into consideration the current user permissions
• The list of active versions can now be overridden from .com to include versions granted by a temporal access.

Some notes:

• We are returning some custom 404 responses, but DRF already handles that when using get_object_or_404. Anyway, users won't see any of the messages, since our 404 handler is catching those in production.
• Returning the full serialized version of translations takes like 40 extra queries, probably it generates more per extra translation. From what I found, most of the queries are due to the serializer returning more related projects fully serialized (main translation, superproject).
• We are allowing users to override the whole response, we should just allow to override the addons key.
• This also suffers from https://github.com/readthedocs/readthedocs-corporate/issues/1845

Since to really run the whole code from permissions checks organizations are needed, I'll add tests on .com.

ref https://github.com/readthedocs/readthedocs-corporate/issues/1773

[stsewd]

This is still missing tests, but those will be in .com, and this PR won't change much. So, marking it as ready for review.

[humitos]

Looks good to me. I just left a few suggestions and comments 👍🏼

[humitos]

There is no need to receive the request here and passing it to the other methods. We just need the user; which is the only attribute we are using from the request.

[stsewd]

A request object is needed for .com,see https://github.com/readthedocs/readthedocs-corporate/pull/1857.

[humitos]

Why do we need the main_language_project as select related here? Where is it used?

[stsewd]

It's used in the serializer, we are doing lots of n+1 queries there.