main/rdiff-backup: get version with importlib-metadata

If py3-setuptools is not installed 'rdiff-backup --version' will just report DEV, this adds py3-importlib-metadata as an option to installing py3-setuptools.

backport from upstream/master

added 2 commits

• 55c34d99 - 1 commit from branch alpine:master
• 9c1524ec - main/rdiff-backup: get version with importlib-metadata

Compare with previous version

merged