Resolve Markdown unordered lists not conforming to styleguide

What does this MR do?

The GitLab documentation style guide requires that unordered lists items are always prefixed with -.

Standards are good, but may places in the documentation suite don't follow the standard.

This MR:

• Fixes most (if not all) instances of unordered lists not adhering to the style guide.
• Other markdown or grammar issues if they are located near a list fix.

Related issues

Ported by: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8437.

Relates to: https://gitlab.com/gitlab-com/gitlab-docs/issues/287.

Author's checklist

• Apply the correct labels and milestone
• Port the MR to EE (or backport from CE): always recommended, required when the ee-compat-check job fails

Review checklist

• Your team's review (required)
• PM's review (recommended, but not a blocker)
• Technical writer's review (required)
• Merge the EE-MR first, CE-MR afterwards