Expose HEALTHCHECK method to Dockerfile task

[marcospereira]

Closes #1204.

What?

This adds a new instruction to support HEALTHCHECKs:

https://docs.docker.com/engine/reference/builder/#healthcheck

Users will be able to configure health checks by declaring tasks such as:

task createDockerfile(type: Dockerfile) {
    ...
    healthcheck(
      new Dockerfile.Healthcheck('/bin/check-running')
        .withTimeout(Duration.ofSeconds(10))
        .withInterval(Duration.ofSeconds(20))
        .withRetries(10)
    )
}

Resulting in:

...
HEALTHCHECK --timeout=10s --interval=20s --retries=10 CMD /bin/check-running

[bmuschko]

Thanks for providing the pull request. Looks solid!

[bmuschko]

I'll change that on my end.

[marcospereira]

Thanks for the quick merge/release, @bmuschko! 🎉