Add 'labels' input

[ntkme]

This PR adds support for "labels" input to support automatically generated labels from docker/metadata-action

Checklist

• [x] This PR includes a documentation change

• [ ] This PR does not need a documentation change

• [x] This PR includes test changes

• [ ] This PR's changes are already tested

• [ ] This change is not user-facing
• [ ] This change is a patch change
• [x] This change is a minor change
• [ ] This change is a major (breaking) change

Changes made

[tetchel]

is there any reason to split by newline instead of whitespace? can labels contain spaces?

[ntkme]

@tetchel The value of label may contain normal space characters. E.g. org.opencontainers.image.description=This your first repo!

[ntkme]

@divyansh42 Sure. Let me rebase first and add that.