ChatOps used to be in the Ultimate tier.

Originally submitted at
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3056

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Signed-off-by: Rémy Coutable <remy@rymai.me>

Prefer index.md instead since they provide clean URLs in the docs site

Signed-off-by: Rémy Coutable <remy@rymai.me>

All this does is convert the version sections into headers. The list
items shouldn't really be indented by two spaces, but it makes no
difference to the rendering and this way we retain authorship history
for the actual changes.

Related to https://gitlab.com/gitlab-org/release-tools/merge_requests/29