Allow to add deploy keys with write-access

Closes #1376

See merge request !7383

Fix broken test

Remove spinach tests for the builds tab

* upstream/master: (538 commits)
  Reject blank environment vcariables in Gitlab::Git::RevList
  Add online terminal documentation
  Add changelog entry
  Add terminal UI and controller actions
  Fix specs
  Even out padding on plus button in breadcrumb menu
  Update font size of detail page header to 14px
  Update CHANGELOG.md for 8.13.10
  Update CHANGELOG.md for 8.14.5
  Fix Route#rename_children behavior
  Remove inline-block styling from status
  Add terminals to the Kubernetes deployment service
  Add a ReactiveCaching concern for use in the KubernetesService
  Add xterm.js 2.1.0 and a wrapper class to the asset pipeline
  Remove unnecessary hidden svg elements for icons.
  Fix consistent typo in environment.js
  Use a block to insert extra check for authenticate_build!
  Align milestone column header with count number
  Add Wiki import to BB importer
  Make CI badge hitboxes better match container
  ...

Move admin projects spinach tests to RSpec

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/23036

See merge request !8174

Slack slash commands

## What does this MR do?

Implement Slack Slash Commands by utilizing generalized Mattermost presenter to fulfill Slack requirements.

## Why was this MR needed?

We want to expose Slack Slash Commands as a first-class service.

## What are the relevant issue numbers?

Supersedes !8007  
Closes #22182

See merge request !8126

Move Admin Appearance spinach feature to RSpec

Part of #23036

See merge request !8063

Move admin labels spinach test to RSpec

Part of #23036

See merge request !8166