Square and Angle bracket use causes kramdown warnings,
so changed or enclosed in backticks as needed

Update capitalization in /administration, /api, /ci
and /customization

Code blocks should not be spaced 4 times, as this will
prevent the code from being colored. They should
also be spaced the same as the lists they are a part
of, to make reading easier.

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

After review, heading was changed and links to
it needed to be updated, and minor tweaks to
the issues docs such as note formatting

* (Suf)fix #51085 :-)

Signed-off-by: Samuele Kaplun <kaplun@protonmail.com>

Split into user and administrator docs:

- administration/issue_closing_pattern.md
- user/project/issues/automatic_issue_closing.md

[ci skip]