Organize dependency build processes

[dervoeti]

Implementation of https://github.com/stackabletech/decisions/issues/44

Tasks:

• Migrate all mirrored sources from Nexus to GitHub repositories. Update the “upload new version” process, which currently relies on shell scripts, to use GitHub instead. Ensure all historical versions are preserved if necessary.
• Organize the folder hierarchy for dependencies (such as kcat, Phoenix, and hbase-connectors). Decide whether to place them at the top level (alongside products) or in a dedicated dependencies/ subdirectory.
• Ensure each dependency has its own dedicated Dockerfile. Dependencies should be copied into our products using COPY --from. Modify relevant build processes (e.g., patch pom.xml to reference local JARs).
• Apply a standardized SDP version suffix (3.4.1-stackable25.3.0) to all SDP artifacts that include custom modifications. This applies to JARs, Go binaries, Python packages, container images, etc.
• Ensure vulnerability scanners continue detecting the original upstream version (e.g., 3.4.1 for Hadoop). This may require adding metadata, dummy components, or another approach.

Non-Goals:

• Publishing artifacts (e.g., JARs in a Maven repository) is out of scope for this issue. This will be addressed when implementing stackabletech/issues#674.