[WIP] docs/ci: Add link redirect checker to CI

[phlax]

Signed-off-by: Ryan Northey ryan@synca.io

Commit Message: docs/ci: Add link redirect checker to CI
Additional Description:

Now that we have added sphinxext-rediraffe we can use its tool to detect if a page has been moved in docs, without adding a redirect link for it

Risk Level: low
Testing: yep
Docs Changes:
Release Notes:
[Optional Runtime guard:]
[Optional Fixes #Issue] touch #13436
[Optional Deprecated:]

[phlax]

initial testing didnt trigger the diff error - need to test a bit further

[phlax]

also, not entirely clear how this will work in terms of sphinx and our path mangling - my first reading of the source in rediraffe is that there is an assumption that sphinx is run from root - but this might be wrong. Either way i need to play with this a bit further outside of envoy repo (added https://github.com/phlax/sphinxdev)

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in 7 days if no further activity occurs. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in 7 days if no further activity occurs. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!

[github-actions]

This pull request has been automatically closed because it has not had activity in the last 37 days. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!