Edited To-Do List for CTRT

What does this MR do?

This MR edits the topics on the page to be tasks or reference topics. It takes content and puts it under titles that apply only to the content beneath the title. (Sometimes content under a heading can start spreading into another topic, and these should be separate.) It also removes extra words and fixes Vale issues.

Specifically:

• I updated the first heading's title to remove the word "GitLab," since we're already in the GitLab help.
• I removed the topic about filtering, since users will just filter by using the UI. No one would search the documentation for filtering unless there were something quirky, different, or unexpected about it. I did leave in a note about filtering by "directly assigned," because that is a bit of a hidden use case. Otherwise a user will just play with the UI until they get the results they want.
• I removed a few lines about how the to-do list icon lists the number of to-dos you have, because a user can see that in the UI and so it doesn't need to be reiterated in the help.
• I removed a bit of marketing language: being able to get started quickly is important. We just want to be able to quickly jump into the docs and find the help they need. This extra info isn't necessary.

Related issues

Related to: #327171 (closed)

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• Ensure that the product tier badge is added to doc's h1.
• Request a review based on the documentation page's metadata and associated Technical Writer.

To avoid having this MR be added to code verification QA issues, don't add these labels: feature, frontend, backend, ~"bug", or database

Review 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.
  • 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 above reviews. Maintainer's review can occur before or after a technical writer review.
• Ensure a release milestone is set.