Use buildx tooling instead of docker API

[devinrsmith]

Historically, we've produced a set of "base" images for deephaven-core to consume as part of the build / integration testing process:

https://github.com/deephaven/deephaven-base-images
https://github.com/deephaven/deephaven-server-docker

The benefit is that developers don't need to worry about building these images themselves; there was a lot of gradle + docker cache issues that caused developer pains without the pre-built base images. Additionally, we weren't able to use this infrastructure to build production docker images since the docker API at this level does not support multi-architecture images.

Given that deephaven-core isn't responsible for our producing our docker images anymore, we may be able to go back to building these images ourselves if we can solve the caching issues.

One way to solve this might be to use more direct / modern docker tooling (buildx) as part of the build instead of using the more limited docker API; this would match the tooling we use for production images.