Improve redirect handling

[elsloo]

• Do not permit a 302 to be cached if a redirect is in progress.
• Could be more permissive if we remove the check for HTTP_STATUS_MOVED_TEMPORARILY in HttpTransact::is_response_cacheable()
• Refactor HttpSM::is_redirect_required() to make it easier to call when state is incomplete
• May address issue #10955

[elsloo]

Changing this PR to a draft until I complete testing and add the AuTests to this PR with a description of what it solves. Without this PR we have corner cases that can lead to a 302 being cached unintentionally, which then leads to secondary problems due to the 302 itself being possibly stuck in cache and served to other caches.

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. Marking it stale to flag it for further consideration by the community.