Add support to add changelog entry with version when running from osc service

[rhabacker]

It would be nice if this service would support adding an associated changelog entry when running from osc service runall

If a package has a _service file that fetches tarballs from a git repo, for example, you need to do the following:

1. run service runall
2. copy version to clipboard
3. run osc vc
4. type the line "update to version" and paste the version into the file.
5. save file and close

This could be simplified by a new option for osc service which also updates the change file(s).