Add code to cpp-client/build.gradle to run tests in docker.

[jcferretti]

This does not include yet code to automatically check consistency of generated protos, that should come in a later PR.

Summary of changes:

• Removed build-dependencies.sh, now lives in the deephaven-base-images repository (https://github.com/deephaven/deephaven-base-images/tree/main/cpp-client). The script there is refactored some, to allow for building individual parts. Also made the script write a new env.sh file at the end with environment variables to source for, eg, CMAKE_PREFIX_PATH. Updated README.md to reflect the change.
• In a separate PR for the deephaven-base-images repository, and with a lot of help from Devin (thanks!)
  we have added code to create a "cpp-client-base" image (code here) that contains all the dependent libraries already built
  in ubuntu-22.04. The code added to cpp-client/build.gradle to do checks via docker leans on that to avoid
  having to wait too long and create too many layer of the new image.
• Small change to tests/test_util.cc to support changing the host:port for the server via setting environment variables DH_HOST and DH_PORT, needed for automating the tests.

[kosak]

Some micro-comments.

[devinrsmith]

Just for reference, the base image will be our largest yet, topping in at over 3GB.

deephaven/cpp-client-base                                 local-build       2893a2a398e3   16 hours ago     3.11GB

[jcferretti]

Just for reference, the base image will be our largest yet, topping in at over 3GB.

deephaven/cpp-client-base                                 local-build       2893a2a398e3   16 hours ago     3.11GB

Devin and myself discussed making a docker ARG for image generation setting BUILD_TYPE=Release as default; the build-dependencies.sh script itself is not changing, but the way it is invoked from the dockerfile will change to use the ARG. This results in a more economical image:

cfs@guanaco 15:46:55 ~/dh/oss1/deephaven-base-images
$ docker images | grep cpp-client-base
ghcr.io/deephaven/cpp-client-base                         latest        071706e8d34c   26 seconds ago   689MB

I tried that locally, I am updating the PR for deephaven-base-images right after writing this.