[CI] : add test scripts and enhance CI workflow

[maulik-mk]

This pull request significantly refactors the CI workflow to make Docker image builds more robust and efficient, especially around versioning, label management, and conditional publishing. It also modularizes test asset downloading and test execution into separate scripts, improving maintainability and clarity.

CI Workflow Improvements:

• Added steps to extract the VERSION from the Dockerfile and set a BUILD_DATE environment variable, enabling version-aware builds and metadata tagging.
• Implemented logic to extract all Dockerfile labels, substitute build-time values, and use them in the Docker build process for better image metadata.
• Added a check to skip Docker builds and pushes if the image version already exists in GHCR, preventing redundant work and accidental overwrites.
• Restricted Docker image build and push steps to only run for new major/minor versions on the main branch, aligning with semantic versioning best practices.

Test Automation and Script Modularization:

• Moved the video download logic into a dedicated script (.github/scripts/download_test_video.sh) and the test execution logic into another script (.github/scripts/run_tests.sh), simplifying the workflow YAML and making test steps reusable. [1] [2] [3]

Minor Workflow Cleanups:

• Standardized branch list formatting in workflow triggers for consistency.