Add find key by base64 key or fingerprint to the internal API

See merge request !250

Squashed changes:
Add unique index to fingerprint
Add new index to schema
Add internal api to get ssh key by fingerprint
Change API endpoint to authorized_keys
Add InsecureKeyFingerprint that calculates the fingerprint without shelling out
Add require for gitlab key fingerprint
Remove uniqueness of fingerprint index
Remove unique option from migration
Fix spec style in fingerprint test
Fix rubocop complain
Extract insecure key fingerprint to separate file
Change migration to support building index concurrently
Remove those hideous tabs

On GitLab.com, there are write deploy keys with no associated users.
Pushes with these deploy keys end with an Error 500 since we attempt
to look up redirect message. If there is no user, don't attempt
to display a redirect message.

Closes #41466

- Better gitaly-handling in /api/internal/allowed specs

Signed-off-by: Rémy Coutable <remy@rymai.me>

Remove superfluous lib: true, type: redis, service: true, models: true, services: true, no_db: true, api: true
Signed-off-by: Rémy Coutable <remy@rymai.me>

Somehow Rails.cache.fetch occasionally returns `nil` values, which causes
this endpoint to crash.

Closes #35094

- Make single gitaly payload
- Add feature-flag specs to verify payload

This new param allows us to share project information between components
that don't share or don't have access to the same filesystem
mountpoints, for example between Gitaly and Rails or between Rails and
Gitlab-Shell hooks. The previous parameters are still supported, but if
found, gl_repository is prefered. The old parameters should be deprecated
once all components support the new format.

Removed all the unnecessary include of `WaitForAjax` and `ApiHelpers` in the specs.
Removed unnecessary usage of `api:true`

This new class uses a Redis Hash instead of a Sorted Set.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Refactored specs and added a post deployment migration to remove the activity users table.

It uses a user activity table instead of a column in users.
Tested with mySQL and postgreSQL

Signed-off-by: Rémy Coutable <remy@rymai.me>