Restrict failed login attempts from users with 2FA enabled.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/19799.

See merge request !6668

Copy logic from `Devise::Models::Lockable#valid_for_authentication?`, as
our custom login flow with two pages doesn't call this method. This will
increment the failed login counter, and lock the user's account once
they exceed the number of failed attempts.

Also ensure that users who are locked can't continue to submit 2FA
codes.

Save a fetchable ref per deployement

cc @DouweM @ayufan

See merge request !6618

Fix bug when trying to cache closed issues from external issue trackers

fixes #22446

See merge request !6619

Simplify Mentionable concern instance methods

## What does this MR do?

Simplify arguments received by the instance methods on the concern so in the closer future will be easy to understand and change

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

See merge request !6596

We remove some arguments that are rarely used or 
used just to simplify setups on specs.

Modified Mentionable#create_new_cross_references method 
we don’t need to calculate previous references to avoid the 
duplication because we do that at database level when 
creating references extracted from the current entity state.

MergeRequests won’t create cross_references for commits that are included so we change a spec to use a different merge request to make references to commits to other branches