Use Bodhi not (orphaned) pkgdb for current release info (#17)
Until now we've used
https://admin.fedoraproject.org/pkgdb/api/collections/ as our
source of truth for deciding what Fedora releases exist and what
state they're in (for the purposes of `get_current_release()`
and `get_current_stables()`). This used to be an API endpoint of
the pkgdb webapp; in 2017 pkgdb was retired, but because we and
GNOME Software (and possibly some other things) were still using
it, releng kept this specific URL active and serving a static
JSON-formatted text file that has to be updated by hand each time
we branch, cut a stable release, or EOL a release.
Unsurprisingly, this doesn't always happen perfectly on time, or
without mistakes (recently, F32 was added but initally marked as
'stable' rather than 'development', for instance). So to avoid
such problems, and hopefully to help releng eventually retire
this silly hack, let's port off it and use the Bodhi 'releases'
API instead. It provides all the information we need, and as
it's a real API of an important system, should be updated on time
and with correct data reliably.
Signed-off-by: Adam Williamson <awilliam@redhat.com>