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Also, add gnome-tour to tarball-conversion

Link to: https://gitlab.gnome.org/Teams/Releng/freeze-breaks

most of the remaining things are hosted on github, with a few on
freedesktop gitlab, sourcforge or have a weird layout. Those will
need a new plugin.

Part of #11

https://gitlab.gnome.org/Infrastructure/sysadmin-bin/-/blob/78880cd100f6a73acc9dbd8c0dc3cb9a52e6fc23/ftpadmin#L88-141

This doesn't belong here!

One of our mirrors has started rate-limiting us. It seems this mirror is
selected for me 100% of the time, and tarball conversion fails 100% of
the time. Ouch. We can avoid this by sleeping for one second and
retrying when it occurs.

Note this is called on a thread, so it theoretically only affects the
thread that actaully received the 429 response. This means that other
threads are likely to hit the same error, but that's OK.

Fixes #23

This replaces deprecated optparse with argparse.

It also changes the syntax of how to specify the directory. Instead of
passing -d, the directory must now be passed as the final positional
argument to the script. This makes sense, because it is mandatory, and
using options for mandatory things is confusing.

This also removes the need to pass a version when using --no-convert

Fixes #22