Add opencontainers labels to the renovate/renovate docker image

[mikebryant]

What would you like Renovate to be able to do?
We're building our own docker image of renovate to add configuration / internal certificate authorities etc.

We want to use renovate to automaticlly update the base image. #2907 allows renovate to find the source from a docker image if labels are supplied.

Describe the solution you'd like
Add the org.opencontainers.image.source label (and optionally the other ones that are part of the standard) to the renovate/renovate docker image on dockerhub.

Currently the labels are:

$ docker inspect renovate/renovate:17.7.9 | grep -i labels -A 3
            "Labels": {
                "maintainer": "Rhys Arkins <rhys@arkins.net>",
                "name": "renovate"
            }

Describe alternatives you've considered
Haven't considered alternatives

[renovate-bot]

🎉 This issue has been resolved in version 17.8.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀