Generate static delta after OSTree commit

After generating the commit, we can use the tip of the branch to generate the static delta that exactly matches the commit. Use image_name as the name of the static delta to help distinguish between each other when in a repository. The name also contains the pipeline version in the name, hence it is possible to sort by filename to get the most recent static delta.

Signed-off-by: Frédéric Dalleau frederic.dalleau@collabora.com