DAST add redirects

What does this MR do?

Brief description

• Add 6 files missed in a previous MR.
• Put in place redirections for all files moved in Reorganize browser based DAST documentation (!138868 - merged)

These redirections are being put in place in GitLab 16.9, so according to the redirection convention, they're eligible to be removed on May 16, 2024, the release date of GitLab 17.0.

Background

The browser-based DAST tool references the files in the checks directory. All of these files were moved in Reorganize browser based DAST documentation (!138868 - merged), with several exceptions. Between when Mike Eddington started on !138868 (merged) and when it was ready for review and merging, 6 more files were added to the checks directory, but these were not identified at the time.

All the files in the checks directory were moved, so this MR adds a redirection for all these files.

In addition to the files in the checks directory, several related files were also moved, and this MR adds redirections for them:

• dast/browser_based.md moved to dast/browser/index.md
• dast/browser_based_troubleshooting.md moved to dast/browser/troubleshooting.md

Finally, several pages linked to content within the moved files, so this MR updates their links to the new locations.

Related issues

Reorganize documentation for DAST (#429537 - closed)

Author's checklist

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Reviewer's checklist

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