Update the vale internal link extension test

What does this MR do?

As pointed out in the related issue, links without the index.md work when rendered on the docs site, but do not work when viewed from a self-managed instance's /help, or when working on the docs locally.

The vale link check was not catching these links, so this MR updates the test to catch them. Also fixes a few of the links to demonstrate the issue.

MR set as Draft until all other links are fixed in separate MRs.

Regex

This regex looks for links that don't have a : (anything with a : would be an external link, like https://example.com), and then looks for:

• .html
• /)
• /#any-anchor)

This would catch all these improper links:

• [deploy token](../deploy_tokens/) (no index.md)
• [deploy token](../deploy_tokens/#anchor) (with anchor, but no index.md)
• [deploy token](index.html) (.html file)
• [deploy token](../deploy_tokens/index.html#anchor) (.html with anchor)

Related issues

• Related to &8484
• Related to !96651 (merged)

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
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  • 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:
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  • 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.