Delete dynamic environments

- Adds "close environment" action to a merge request
- Adds tabs to environments list
- Adds close button to each environment row in environments list
- Replaces Destroy button with Close button inside an environment
- Adds close button to builds list inside an environment

In order to enable stopping environments a valid `.gitlab-ci.yml` syntax has to be used:

```
review:
  environment:
    name: review/$app
    on_stop: stop_review

stop_review:
  script: echo Delete My App
  when: manual
  environment:
    name: review/$app
    action: stop
```

This MR requires that `stop_review` has to have: `when`, `environment:name` and `environment:action` defined.
The next MR after this one will verify that and enforce that these settings are configured.

It will also implicitly configure these settings, making it possible to define it like this:

```
review:
  environment:
    name: review/$app
    on_stop: stop_review

stop_review:
  script: echo Delete My App
```

Closes #22191

See merge request !6669
Signed-off-by: Rémy Coutable <remy@rymai.me>

Environments that can have a URL with predefined CI variables.