Draft: Combined deprecations and removals

What does this MR do?

This MR moves all of the removal yaml files from 15.0 and later into the deprecations folder.

Then, this MR:

• Changes the title of the page and the intro text.
• Moves the big disclaimer to the bottom of the page.
• Changes the sort to be based on the "removal" version, rather than the "announced" version.
• Adds the announced date and puts the announced version in parentheses.

You can see that many entries are duplicates, because people had one yaml file for the deprecation and one for the removal.

This is just a rough draft, so we can see how it might look if everything is combined.

Known issues:

• The filter is broken but can be changed to whatever we need.
• Some milestones don't have entries and this code doesn't account for that.
• Removal yaml files prior to 15.0 don't have an announced_in date. We'll need to add if we want to add those items to this list.
• Maybe instead of "removal milestone" we can just say "milestone." We just want people to know which release the biggest impact occurs.
• We should use an icon or hover for breaking changes, instead of repeating the note over and over again.

Related issues

Related to: gitlab-com/www-gitlab-com#13399 (closed)

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding or changing the main heading of the page (H1), ensure that the product tier badge is added.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.