KAFKA-20087: Automate Docker Images creation workflow

[zooo-code]

Summary

Automates the Docker Release Candidate (RC) creation process.

Currently, release managers have to manually trigger four separate workflows.
This PR chains them into a single pipeline that:

1. Builds/Tests JVM and Native images in parallel.
2. Pushes RC images to DockerHub upon success.
3. Verifies tags on DockerHub.

Changes

• Added .github/workflows/docker_rc_automation.yml: New workflow to orchestrate the pipeline.
• Updated docker/README.md

Implementation Details

Uses GitHub CLI (gh) to orchestrate existing workflows:

• Triggers docker_build_and_test.yml for both JVM and native.
• Once passed, triggers docker_rc_release.yml for pushing images.
• Finally, verifies the tags via DockerHub API.
• Uses gh run watch --exit-status to propagate failures correctly.

Testing

• Validated the orchestration logic (triggering & watching) in my forked repository.
• Note: Full E2E testing wasn't possible as I don't have access to DOCKERHUB_TOKEN secrets.

Related Issue

Resolves KAFKA-20087(https://issues.apache.org/jira/browse/KAFKA-20087)

Thanks!!