AES-256-GCM cipher mode requires a key that is exactly 32 bytes long.
We already handle the case when the key is too long, by truncating, but
the key can also be too short in some installations. Switching to a key
that is always exactly the right length (by virtue of right-padding
ASCII 0 characters) allows encryption to proceed, without breaking
backward compatibility.

When the key is too short, encryption fails with an `ArgumentError`,
causing the web hooks functionality to be unusable. As a result, zero
rows can exist with values encrypted with the too-short key.

When the key is too long, it is silently truncated. In this case, the
key is unchanged, so values encrypted with the new too-long key will
still be successfully decrypted.

In EE this method takes an additional argument that specifies the name
of the hook to trigger. There is no particular reason to not backport
this to CE, since by default the behaviour remains the same. By
backporting this code we remove the need for prepending ServiceHook with
a module in EE.

Add RuboCop cops to enforce code reusing rules

See merge request gitlab-org/gitlab-ce!21391

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

Partially addresses #47424.

Allow specificying a branch filter for a project hook and only trigger
a project hook if either the branch filter is blank or the branch matches.
Only supported for push_events for now.