tools: add git-version-next script release versioning

tools: add git-version-next script release versioning

- Only works on stable/* branches (releases are generated from stable branches)
- Supports util-linux versioning: vX.Y (major), vX.Y.Z (maintenance)
- Command-line options: --rc, --release-master, --release-update
- Safety check prevents --release-master on branches with existing releases
- Testing support via --last-release and --last-xy-release overrides

Version Schema:
  Major releases:      vX.Y-rc1, vX.Y-rc2, [vX.Y-rc3], vX.Y
  Maintenance releases: vX.Y.Z-rc1, vX.Y.Z

Signed-off-by: Karel Zak <kzak@redhat.com>