Previously, we used brackets to denote the tier badges,
but this made Kramdown, the docs site Markdown renderer,
show many warnings when building the site. This is now
fixed by using parentheses instead of square brackets.

This was caused by [PREMIUM] looking like a link to
Kramdown, which couldn't find a URL there.

See:
- https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/484
- https://gitlab.com/gitlab-org/gitlab-ce/issues/63800

When this option is enabled, GitLab will create namespaces and service
accounts as usual. When disabled, GitLab wont create any project
specific kubernetes resources

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56557

Domain was introduced on 11.8 and was not included on the
Project Cluster API. With this change user will be able to include
domain when adding and updating a cluster. Domain will also be included
on the GET calls.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/59441

Project cluster API was included on 11.7. This MR describes the new
project cluster endpoints