These changes align the docs with the features introduced in [1].

See also the [issue tracking the documentation changes][2].

[1]: https://gitlab.com/gitlab-org/gitlab-ee/issues/10077
[2]: https://gitlab.com/gitlab-org/gitlab-ee/issues/12986

As decided in https://gitlab.com/gitlab-org/gitlab-ce/issues/53593

Also fixes links to section headings that
have changed.

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

https://community.atlassian.com/t5/Jira-questions/Is-it-quot-JIRA-quot-or-quot-Jira-quot/qaq-p/681163Signed-off-by: NTakuya Noguchi <takninnovationresearch@gmail.com>

ChatOps used to be in the Ultimate tier.

This reverts merge request
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21946

Also:

- Replace DevOps image with one with all stages.
- Further restructure page.
- Edit and tabulate lower part of page.

Includes:

- New enhanced overview button.
- Aligning the top table.
- Start of thorough edit and table reorganisation.

- Adding icons.
- Adding more stages.
- Alphabetising tables.
- Adding more links.
- Andother minor improvements.

Includes:

- Orientating page around audiences.
- Adding descriptions to all links.
- Light restructuring.
- Minor fixes.