migrate help.tpo into a gitlab wiki

we are currently using ikiwiki to host our documentation. that has served us well so far: it's available as a static site in the static mirror system and allows all sysadmins to have a static, offsite copy of the documentation when everything is down.

but ikiwiki is showing its age. it's an old program written in Perl, difficult to theme and not very welcoming to new users. for example, it's impossible for a user unfamiliar with git to contribute to the documentation. it also has its own unique Markdown dialect that is not used anywhere else. and while Markdown itself is not standardized and has lots of such dialects, there is /some/ convergence around CommonMark and GFM (GitHub's markdown) as de-facto standards at least, which ikiwiki still has to catchup with. it also has powerful macros which are nice to make complex websites, but do not render in the offline documentation, making us dependent on the rendered copy (as opposed to setting up client-side tools to peruse the documentation).

gitlab wikis, in contrast, have a web interface to edit pages. it doesn't have the macros ikiwiki has, but that's nothing a few commandline hacks can't fix... or at least we should consider it. they don't have macros or any more powerful features that ikiwiki has, but maybe that's exactly what we want.

this is not blocking the trac to gitlab migration, but it would be nice to jump onboard with everyone, since we will be migrating the Trac wiki onto gitlab as well...

remaining tasks:

• rewrite content, done with https://gitlab.com/anarcat/scripts/raw/master/ikiwiki2hugo.py
• push new wiki in place, done in https://gitlab.torproject.org/tpo/tpa/services/-/wikis/home, new remote is git@gitlab.torproject.org:tpo/tpa/services.wiki.git
• make old wiki readonly, done in gitolite
• archive old wiki, done in 1,222.9 MB in 23,846 resp. at 4.9/s, archive will be visible in the viewer shortly
• redirect old wiki website, done in ac5de6f4 (redirect help.tpo to the new gitlab wiki (#34437 (closed))) and 62fb2a81 (add redirection for metrics and everything else)
• redirect help.tpo/support to support.tpo, done in 16426ae0 (also redirect /support to support.tpo (tpo/community/support#40002 (closed)))
• tpo/metrics/trac#40001 migrate metrics to their own wiki and redirect redirect done
• cleanup old torhelp user
  • remove gitolite hooks
  • scheduled deletion of the old help.tpo stuff on mirrors for july 1st
  • check for remaining files owned by torhelp
  • remove torhelp sudoers entries (in puppet)
  • delete the user and group from LDAP
• archived old git repositories in https://gitlab.torproject.org/tpo/tpa/wiki-archive and https://gitlab.torproject.org/tpo/tpa/wiki-infra-archive
• redirect old git repository, with pre-receive hooks and description updates
• rename this project to team so it matches the policy discussed in #28 and have the wiki more meaningful and easier to find - postponed to #40021 (closed)
• remove ikiwiki from staticiforme