cgit view availabel

After a short time (ahem, several years) of badgering of me my a
certain community member, I've finally gotten around to putting up a
cgit instance on our git server, to allow for browsing of the git
repositories. You can find this at:

https://git.postgresql.org/cgit/

or specifically for the postgresql git repo:

https://git.postgresql.org/cgit/postgresql.git/

For the time being we're running both this and gitweb, and all the
redirects will keep pointing to gitweb, as well as the default
redirect if you just go https://git.postgresql.org/.

If people prefer it, we can discuss changing that in the future, but
let's start with some proper full scale testing to see that it doesn't
actually just break for some people :)

//Magnus