Hirsute Hippo is now open for development

[Matthias Klose]

Hirsute Hippo is now open for development, with the uploads collected in the
queue now approved, and syncs from unstable enabled.

The development version starts with one change:

 - Python 3.9 is now added as a supported Python3 version, with the
   goal to ship Python 3.9 as the only Python3 version in hirsute.

Please check your uploads in a hirsute chroot, don't just test in a focal or
groovy environment.  See [1] or [2] how to setup such a development chroot.

Some major changes planned for this cycle are mentioned in the Hirsute release
schedule [3].

-- 
[1] https://wiki.ubuntu.com/SimpleSbuild
[2] https://wiki.ubuntu.com/DebootstrapChroot
[3] https://discourse.ubuntu.com/t/hirsute-hippo-release-schedule/18539