The support page is the go-to page for the "how to get help" question,
which previously was hidden inside the TPA-RFC-2 standard.

This basically copies that part of the TPA-RFC-2 policy, but could
eventually diverge without needing to update the policy, for informal
stuff.

I started working on this page while trying to address
#40382 ("document the triage process"), but I'm not
actually sure triage documentation should go there, as this page feels
more targeted at users, and only users.

howto/incident-response.md would seem like a better space for this.

Also, this is a toplevel page because it's more important than
everything else, so it warrants its own special space.

The latter is actually one of two standard file extensions (as per
RFC7763, the other being .markdown). It's also the extension expected
by GitHub, GitLab, and other wiki software.

So for the sake of future-proofing and compatibility, rename all files
to the new name.

This will hopefully not break anything: the file extension is not
present in the rendered version anyways.

Those are more future proof and will work in gitlab.

        Added ticket #8645