Add labels to oci_image

[psalaberria002]

Fixes #47

I would like to have stamping support before merging this PR. I see @alexeagle is working on stamping in #70.

From what I understand, the script that builds the image will need to read the volatile and stable files when stamping is enabled, and do variable substitution for each key (if found). Should I try something like https://github.com/aspect-build/bazel-lib/blob/998ee223690ed07b3dfc31738dae839206bd60b0/lib/tests/stamping/stamper.sh ? Or is there a more native alternative for stamping?

[thesayyn]

I haven't thought about stamping much. let's split labels and stamping into their own PRs. I'd like to have a solid implementation for stamping and support config_setting at the same time.

[psalaberria002]

I haven't thought about stamping much. let's split labels and stamping into their own PRs. I'd like to have a solid implementation for stamping and support config_setting at the same time.

Fair enough. Let me remove the stamping part.

[alexeagle]

nice, thanks!

[thesayyn]

looks like you need to run bazel run //docs:update

[psalaberria002]

looks like you need to run bazel run //docs:update

Done.

[thesayyn]

Thanks!