Change gnome-software git release tag format

[Jeremy Bicha <jbicha ubuntu com>]

Hi,

I'm proposing that we change the git release tag format for gnome-software.

So far, we have been using tags like GNOME_SOFTWARE_3_27_2. That is a
legacy style inherited from years ago (maybe CVS?).

The current recommendation for GNOME modules [1] is a simple 3.27.2
tag. So that is what I recommend.

Some GNOME modules instead use a pattern like v3.27.2 or gnome-software-3.27.2 .

Debian's git-buildpackage doesn't convert underscores to decimal
points when importing a git tag to match the tarball, so switching the
pattern will make things a bit easier for Debian packagers.

[1] https://wiki.gnome.org/MaintainersCorner/Releasing

Thanks,
Jeremy Bicha