Using update_column to store the boolean flag to avoid
any side effects with the current state of the project
instance

Ensure only IDs ending in .git perform git actions

## What does this MR do?

Rails's routing is pretty strange. Previously, `GET /namespace/project/info/refs` would go to the Git HTTP controller (if the redirect for that case was taken out).

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

The specs fail if the redirect is moved to above the Git HTTP routes, removed altogether, or the Git HTTP constraints are changed. But there might still be missing cases.

## Why was this MR needed?

The master build and HTTP cloning were both broken.

## What are the relevant issue numbers?

Closes #18376.

## Screenshots (if relevant)

Nope.

## Does this MR meet the acceptance criteria?

- [x] [not needed] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [not needed] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] (not needed) API support added
- [ ] Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] 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)

See merge request !4558

It doesn't seem possible to set constraints based on format for project
IDs ending in .git, so set the constraint on the ID and ensure the
format is nil to avoid the case where the project ID is something like
project.git.foo.

Adjust the SAML control flow to allow LDAP identities to be added to an existing SAML user.

## What does this MR do?

It correctly lets an existing SAML user to add their LDAP identity automatically at login.

## Why was this MR needed?

A customer had issues with the `auto_link_ldap_user` feature. The flow was not working if there was an account with a SAML identity, but no LDAP identity. GitLab would pick up the correct LDAP person, but due to the order of the flow, that LDAP person was never associated with the user.

## What are the relevant issue numbers?

Fixes #17346 

/cc @dblessing @balameb @stanhu 

See merge request !4498

Make Omniauth providers specs to not modify global configuration

See merge request !4534

Fix wiki linking behavior for markdown wiki pages

Related to #18019 

- As per the documentation in !4372 

## TODO
- [ ] !4432 Have wiki linking behave as per the documentation
    - [x] Move `WikiLinkFilter` specs to the pipeline level
    - [x] Verify current behavior on wiki `show` page
    - [x] Fix current behavior on wiki `show` page
    - [x] Verify current behaviour on wiki preview
    - [x] Fix current behaviour on wiki preview
        - [x] Rewrite all links and get preview links working
        - [x] Make sure all links are on-par with the wiki `show` page
        - [x] TDD `WikiLinkFilter` and get it working
        - [x] Hook `WikiLinkFilter` up
    - [x] Fix tests 
        - [x] Fix `markdown_spec`
        - [x] Fix `wiki` spinach feature
        - [x] Wait for [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/4f50dd2/builds) to pass
        - [x] Make sure all wiki-related pages are working as expected (history, all pages, etc.)
    - [x] Test in different ruby versions
    - [x] GitLab instances hosted on a relative URL
    - [x] Non-markdown rendering formats?
        - [x] RDoc
        - [x] ASCIIDoc
        - [x] Create issues to fix things for RDoc and ASCIIDoc
    - [x] Gauge performance impact
    - [x] Refactor
    - [x] Re-organize commits
    - [x] Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/f860e9a8dcabe7d5f160c32fc549807c98baa4a1/builds) passes
    - [x] Respond to @rymai's comments
        - [x] `class WikiLinkFilter < HTML::Pipeline::Filter`
        - [x] blank line after guard clause
        - [x] keyword arguments for `wiki` and `slug`
        - [x] invert the condition
        - [x] inline `user` in spec
        - [x] Make sure spec names are not out of date
        - [x] Comment for each rewrite rule
    - [x] Add CHANGELOG entry
    - [x] Reorganize commits
    - [x] Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/19b91e749a6320d12fb299d33f1f6440777e0e26/builds) passes
    - [ ] Wait for merge

See merge request !4432

- Need to pass in a `page_slug` to the filter, so it can rewrite based
  on the current page (all links are rewritten to the level of the app root).
- The earlier `markdown_preview` endpoint was at the level of the wiki.
  We need to know the current page (for rewriting, as above), so this
  commit moves the endpoint to the level of a wiki page.
- Fix all tests