make airbyteDocker build cache functional

[edgao]

What

We're currently rerunning the docker build unnecessarily. This change fixes how we detect image changes after some recent Dockerfile structure updates.

How

• This PR added some COPY --from=build ... directives to our Dockerfiles. The gradle task interpreted this as a dependency on an image called build, which obviously doesn't exist - the task now correctly resolves that image alias
• This PR updated the Dockerfiles to respect a JDK_VERSION environment variable. The gradle task now correctly resolves that environment variable, rather than trying to find a image literally named openjdk:${JDK_VERSION}-slim.

[tuliren]

Nice!

Do we know the amount of build time improvement from this change?

Would you like to present this in the dev meeting?

[sherifnada]

is it possible to implement some sort of unit test for these functions? would be helpful to know when there's a regression in the cache functionality as it can be tricky to hunt down/detect

[edgao]

@tuliren each docker image takes about 1 minute to build. base-normalization spends about 5 minutes building docker images, though presumably if you're making changes + rerunning tests, you have to rebuild at least one of those images. Happy to present at a dev meeting (but not the one next monday, since sherif raises a good point)

@sherifnada makes sense, it looks like there's some sort of test ability (https://docs.gradle.org/current/userguide/custom_tasks.html#sec:writing_tests_for_your_task_class). I'll see if I can get something set up. Really the problem is that we're parsing dockerfiles in a pretty sketchy way, but I couldn't immediately find a (well-maintained) dockerfile parsing library for java 🤷

[jrhizor]

Longer term, I'd recommend considering using a better method of building the docker images than airbyteDocker. For platform builds we've switched to using the bmuschko Docker plugin which should have better caching behavior.

[edgao]

groovy unit tests look messy + we want to use a different plugin anyway; merging this as-is.