Add a packaging Git commitId/Tag reference to Docker images

[oleg-nenashev]

Currently there is no way to reliably track down which version of https://github.com/jenkinsci/docker was used to package the image. It would be great to inject a file to the Docker image which references the commit ID or, later, a tag.

Such information can be used by users to track down changes, especially for weekly releases when changelogs from #856 are not available

[glefloch]

@oleg-nenashev I would like to work on this. Couldn't we just add a label on the image ? if you prefer a file, where should we put it and how do we name it?

[oleg-nenashev]

@glefloch label would be even better, you are right

[hjwk]

is this issue still valid ?

[timja]

yes