Upgrade osgeo6 to buster

[robe]

Right now osgeo6 is at debian stretch level. Which is two stable versions behind. I had meant to do this last year.

My main concern is with the mailing system. When I had upgraded trac to buster the mail stopped working (I mean the mail server was working as far as I could tell, but trac couldn't use it) and I hadn't investigated why, Instead I just put in a stop gap to channel email thru osgeo6.

Given that osgeo6 is our primary mail server, special attention must be given to make sure it doesn't happen and that lists still works after, and other services that channel mail thru it (osgeo.org, repo.osgeo.org, limesurvey.osgeo.org, talks.osgeo.org, trac.osgeo.org, weblate.osgeo.org, wiki.osgeo.org ? (wiki might be using itself) ).

After this is done, we should upgrade to bullseye after, but want to wait a month or so after this upgrade before attempting a bullseye upgrade.

[robe]

Also a side note. for some reason osgeo6 has 2 versions of PostgreSQL running on it with PostgreSQL 12 being the only live one (11 is stopped on port 5433). At a glance only the drone database is on the running instance. drone has been moved to dronie-server dronie.osgeo.org, so this old drone is not needed anymore.

I plan to uninstall PostgreSQL completely on osgeo6 before pushing forward with the upgrade.

[robe]

Other thing I plan to remove:

docker -- there are no docker containers running on this server and not sure if there were ever any.