Architecture doc revamp

What does this MR do?

We no longer use reference links within documentation, and are now cleaning them up (see related issue). The architecture page is the page with the largest number of reference links (91). This is entirely due to the large table, which links to each section within the page, but also has links to sections outside the page.

After reviewing the page to find a way to remove the reference links, I realized that all of the links are doubled:

• Once or more in the table
• Again, exact same link, in the section itself further down the page.

As a result, I revamped the table and individual subsections:

• Clean up subsections so that the links can be put in-line easily.
• Move all links to be inline within each subsection, removing the link references.
• Alphabetize table

Related issues

Related to #212770 (closed)

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• If applicable, update the permissions table.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.