Changes

feat(pipelines/pingcap/tiflow): add MariaDB source for DM integration test (#4496)

## Summary

Add MariaDB 12.2 as a sidecar for DM integration tests (classic and
next-gen).

- Add MariaDB 12.2 container (1C/2G) to
`pod-pull_dm_integration_test.yaml`
- Add MariaDB health check (port 3308) and
`MARIADB_HOST1`/`PORT1`/`PASSWORD1` env vars to
`pull_dm_integration_test.groovy` (classic) and
`pull_dm_integration_test_next_gen.groovy` (next-gen)
- Both classic and next-gen pipelines share the same pod template, so
one container addition covers both

## Related

- DM-side PR: pingcap/tiflow#12599 (adds `mariadb_source` test case,
currently excluded from groups until this CI PR is merged)

## Notes

- This PR should be merged before adding `mariadb_source` to a test
group in tiflow.

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
 (commit: a7c5a9e)