We also try to use instance variable to cache the result if
RequestStore is not available, so we could keep the same logic,
using the same cache key. Also introduce a way to specify method
specific cache key
I don't like the idea of `RequestStore` at all, because it's just a
global state which shouldn't be used at all. But we have a number of
places calling `ProtectedBranch.protected?` and `ProtectedTag.protected?`
in a loop for the same user, project, and ref whenever we're checking
against if the jobs for a given pipeline is accessible for a given user.
This means we're effectively making N queries for the same thing over
and over.
To properly fix this, we need to change how we check the permission,
and that could be a huge work. To solve this quickly, adding a cache
layer for the given request would be quite simple to do.
We're already doing this in Commit#author, and this is extending that
idea and make it generalized.
