Cache bust and update GH Actions Workflow cicd.yml to bust EWTS Docker cache when remote ref changes

[cmaynard-ngwpc]

• Optimized Docker build caching
  • Added build args for ESMF and GDAL versions so their layers rebuild only when the version changes.
  • Introduced cache-busting args for EWTS, ESMF, and GDAL to allow targeted rebuilds of those layers when needed.
• Improved CI/CD handling of EWTS builds
  • Updated GitHub Actions workflow to resolve EWTS_REF to its commit SHA and pass it as the EWTS_CACHE_BUST build arg.
  • Ensures the EWTS Docker layer rebuilds when a branch/tag HEAD changes, while preserving cache stability when using fixed commit hashes.