CI: consolidate Rocky 8/9/10 workflows into single matrix-driven file

Replace three separate Rocky Linux CI workflow files with one
matrix-driven workflow that runs build + test across Rocky 8, 9, 10.

Key changes:
- New file: .github/workflows/build-cloudberry-rocky.yml
- Remove: build-cloudberry.yml (Rocky 9), build-cloudberry-rocky8.yml,
  build-cloudberry-rocky10.yml
- PR trigger: all three Rocky versions now run on every PR (was only
  Rocky 9 before; Rocky 8/10 only triggered on push to main)
- Remove scheduled cron trigger (push + PR coverage is sufficient)
- Test matrix: union of all test suites across versions; every test
  now runs on every Rocky version, including ic-recovery, ic-diskquota,
  ic-orca-parallel, and gp_relsizes_stats
- Container images and --releasever now resolved dynamically via
  matrix.rocky_version
- Artifact names consistently suffixed with -rocky${{ version }}

See: http://github.com/apache/cloudberry/discussions/1696
Assisted-by: Deepseek

Author: tuhaihe