feat: include source code of operators

[dervoeti]

Description

Last thing missing for #1069
This includes the operator source code in the container images. Or really: it will place an archive with the source code of anything built with ubi9-rust-builder inside the /app directory, just like copy_artifacts.sh does it for the generated SBOMs.

Additional fix: Merge two build stages in the Hadoop builder. The separation of these was accidentally introduced by #1186

Definition of Done Checklist

Note

Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant.

Please make sure all these things are done and tick the boxes

• Changes are OpenShift compatible
• All added packages (via microdnf or otherwise) have a comment on why they are added
• Things not downloaded from Red Hat repositories should be mirrored in the Stackable repository and downloaded from there
• All packages should have (if available) signatures/hashes verified
• Add an entry to the CHANGELOG.md file
• Integration tests ran successfully

TIP: Running integration tests with a new product image

The image can be built and uploaded to the kind cluster with the following commands:

bake --product <product> --image-version <stackable-image-version>
kind load docker-image <image-tagged-with-the-major-version> --name=<name-of-your-test-cluster>

See the output of bake to retrieve the image tag for <image-tagged-with-the-major-version>.