Improve performance for fetching active branches and prebuilds

[gtsiolis]

Problem to solve

Back in #4970 we added Branches and Prebuilds pages for Projects.

However, these pages fetch a great amount data from third party providers which adds a noticeable delay during page load.

Proposal

One improvement could be to add a loading state for fetching active branches and prebuilds.

Ideally, we could introduce some mechanisms to make this loading faster, like caching. Looping in @AlexTugarev because of the relevant discussion (internal).

Follow up issue from #4958, point 15. See also #4876 (comment).

[stale]

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