Add setting that allows admins to choose which Git access protocols are enabled.

## What does this MR do?

It allows admins to disable one of the two protocols for Git access. They can choose to enable just SSH, HTTP or allow both. If one of them is disabled, the clone URL in the project will show only the allowed protocol, and no dropdown to change protocols will be presented.

## What are the relevant issue numbers?

Full implementation on GitLab's side for #18601 

GitLab Shell implementation: gitlab-org/gitlab-shell!62

GitLab Workhorse implementation: gitlab-org/gitlab-workhorse!51

## Screenshots (if relevant)

![Screen_Shot_2016-06-16_at_12.26.19_PM](/uploads/bad845142e9704a7385b2eaca51fd4eb/Screen_Shot_2016-06-16_at_12.26.19_PM.png)
![Screen_Shot_2016-06-20_at_4.24.54_PM](/uploads/6e452dd269e06f0be23841ce93866ed6/Screen_Shot_2016-06-20_at_4.24.54_PM.png)



/cc @jschatz1  this MR touches the UI. Please review.

See merge request !4696

Rename ENV['PROTOCOL'] to ENV['GL_PROTOCOL'] to conform to what GitLab Shell expects and make the `protocol` param in `GitAccess` mandatory.

Instrument Rinku usage

## What does this MR do?

Add metrics instrumentation to Rinku, module methods (autolink)

## What are the relevant issue numbers?

#18593 

## Does this MR meet the acceptance criteria?

- [x] [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~~
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5063

Bump Rinku to 2.0.0

## What does this MR do?

Update Rinku gem to last stable version.

## What are the relevant issue numbers?

#18593 

## Does this MR meet the acceptance criteria?

- [x] [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~~
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5064