[10.3] Migrate `can_push` column from `keys` to `deploy_keys_project`
See merge request gitlab/gitlabhq!2276
(cherry picked from commit f6ca52d31bac350a23938e0aebf717c767b4710c)
1f2bd3c0 Backport to 10.3
This is allowed for existing instances so we don't end up 76 offenses
right away, but for new code one should _only_ use this if they _have_
to remove non database data. Even then it's usually better to do this in
a service class as this gives you more control over how to remove the
data (e.g. in bulk).
In 8278b763d9 the default behaviour of annotation
has changes, which was causing a lot of noise in diffs. We decided in #17382
that it is better to get rid of the whole annotate gem, and instead let people
look at schema.rb for the columns in a table.
Fixes: #17382
