One use case for this is manually setting the "action" tag for Grape API
calls. Due to Grape running blocks there are no human readable method
names that can be used for the "action" tag, thus we have to set these
manually on a case by case basis.

To reproduce:

1. Create a project with some content
2. Rename the project
3. Create a new project with the same name.
4. Boom - 404.

After step 2, the branch and tag counts were not being cleared. This would
cause `repository.has_visible_content?` to erroneously return `true`
for the newly-created project.

Closes #13384

If the measure method uses Transaction.current directly the SQL
subscriber (Subscribers::ActiveRecord) will add timings of queries
triggered by DB cleaner.

This makes it easier to query, simplifies the code, and makes it
possible to figure out what transaction the data belongs to (simply
because it's now stored _in_ the transaction).

This new setup keeps track of both the real/wall time _and_ CPU time
spent in a block, both measured using milliseconds (to keep all units
the same).

Closes #15128

Only usage got removed in !3442

This allows us to track how much time of a transaction is spent in
dealing with cached data.

This commit attempts to change default user search scope if otp_user_id
session variable has been set. If it is present, it means that user has
2FA enabled, and has already been verified with login and password. In
this case we should look for user with otp_user_id first, before picking
it up by login.