A11y audit: Accessible name missing

What does this MR do and why?

Fix some a11y issues for Accessibile name missing via GitLab Duo custom A11y workflow:

Using a custom GitLab Duo a11y workflow to identify and fix a11y issues.

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• https://gitlab.com/gitlab-org/gitlab/-/issues/518906+ (false positive, was fixed via Content editor: Add missing aria-label (!179013 - merged))
• https://gitlab.com/gitlab-org/gitlab/-/issues/518931+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518929+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518920+ (false positive, was fixed via Monitor settings: Fix a11y issue with labels (!179074 - merged))
• https://gitlab.com/gitlab-org/gitlab/-/issues/518913+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518912+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518911+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518909+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518907+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518900+
• https://gitlab.com/gitlab-org/gitlab/-/issues/518896+ (false positive, was fixed via Add accessible name for group onboarding form i... (!179001 - merged))
• https://gitlab.com/gitlab-org/gitlab/-/issues/518892+ (false positive, was fixed via Verification: Add missing id for form label to ... (!179079 - merged))

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

Related to #499697 (closed), #517665 (closed), #512691 (closed)