Make release updating happen in add_package_to_database

[Kixiron]

Currently we have three separate parts of adding and fully recognizing a new release, add_package_to_database, update_search_index and update_release_activity. These should all be able to be combined, which would remove two side services (both updaters run on separate threads) and make publishing releases more responsive for users

[Nemo157]

update_search_index writes crates.content which appears to be unused since #721 so it can probably just be dropped and this function deleted.

update_release_activity I assume is for the chart on https://docs.rs/releases/activity, those queries look simple enough, and that page is requested rarely enough, that I don't think those calculations need caching, they could just be done when that page is loaded. (Especially if rewritten to be a single query as I think it can be).

[Kixiron]

Closed by #804