This commit changes how we eager-load projects, routes, and namespaces
required by the deploy keys endpoint, getting a 10x improvement in my
local testing.
The endpoint still doesn't scale in-general, but going from ~13 seconds
to dump a 63K result to generating the same thing in ~1.6 seconds seems
like a good improvement to me.
[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
