Use dynamic HAF image detection instead of hardcoded HAF_COMMIT

Replace hardcoded HAF_COMMIT variable with dynamic detection using
the find_haf_image job from common-ci-configuration. This follows
the same pattern already implemented in HAfAH.

Changes:
- Add source_change_detection.gitlab-ci.yml template include
- Add find_haf_image job in detect stage using .find_upstream_image template
- Remove prepare_haf_image job (replaced by find_haf_image)
- Update prepare_haf_data, sync, and e2e_benchmark_on_postgrest jobs to:
  - Depend on find_haf_image instead of prepare_haf_image
  - Map HAF_UPSTREAM_* variables to HAF_* for compatibility

The find_haf_image job fetches source patterns from HAF's
source-patterns.sh to determine which commits need rebuilds,
ensuring the detection logic stays in sync with HAF.