Time tracking API

Closes #25861

See merge request !8483

Backport timetracking to CE

See merge request !8195

Allow users to seed the initial runner registration token using an environment variable

## What does this MR do?
Allow users to seed the initial runner registration token using an environment variable

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

- Naming, do we want to make sure we are clear it's the 'registration' token. Like GITLAB_RUNNER_REGISTRATION_TOKEN vs what I have now, GITLAB_RUNNER_TOKEN
- Not sure we've tested a seed fixture before, I just made up a directory structure for the test

## Why was this MR needed?

At the moment I want to use this in our idea to production demo:  https://gitlab.com/gitlab-org/gitlab-ce/issues/22190

This is useful for when runner is bundled with gitlab, like in a kubernetes stack, and we want the runner to be able to register with gitlab as soon as they both come up.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] 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)

See merge request !6642

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Add nested groups support on data level

## What does this MR do?

- [x] Add  `parent_id` field to `Namespace`model. 
- [x] Create new database table `routes` that keeps information about full path to each group or project
- [x] Remove uniq index from `namespaces.path`
- [x] Add uniq index on `routes.path`
- [x] Fill routes table with path data from namespaces and projects
- [x] Change Namespace/Project URL lookup by routes table
- [x] Rename related routes (nested groups, projects) when parent path changes

This is solely backend preparation. UI, Permissions and API support will be added in separate merge request.   
 
## Are there points in the code the reviewer needs to double check?

migrations, Route model, Routable concern

Will require downtime. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7121#note_19490281 discussion

## Why was this MR needed?

One step further to full nested groups support

## Screenshots (if relevant)

No UI changes in this merge request so far

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added~~
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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 it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/2772

See merge request !7121

Refine pipeline stages

## What does this MR do?

Introduces a concept of `Ci::Stage` to make it easier to have detailed statuses.

## Why was this MR needed?

This is needed to simplify the handling of `Ci::Statuses` and make the `Stage` actual concept in code:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7889

See merge request !7927