Updated screenshots about description templates in the project
settings documentation.

Closes #https://gitlab.com/gitlab-org/gitlab-ce/issues/65738

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

Also adds and one linting rule
and makes project conform to it.

For the sake of consistency, removes any extraneous
consecutive blank lines from the doc suite.