ci(pingcap-inc): isolate tidb, tiflow, and ticdc jobs (#4349)
## Summary - split dedicated Jenkins and Prow jobs for pingcap-inc/tidb, pingcap-inc/tiflow, and pingcap-inc/ticdc so private repo changes no longer affect pingcap/* jobs - keep only the non-optional release-8.5 TiDB jobs plus pull_integration_e2e_test for pingcap-inc/tidb - reuse the existing scripts instead of copying scripts/pingcap-inc/* - simplify the public pingcap/tidb and pingcap/ticdc pipelines by removing pingcap-inc-specific OCI tag and artifact host branches, except that pingcap-inc/ticdc still keeps the special OCI_ARTIFACT_HOST override only for the TiDB binary download step - enable submodule-aware checkout for pingcap-inc Jenkins jobs, and switch pingcap-inc/tiflow plus pingcap-inc/ticdc Prow presubmits to SSH clone with ssh_key_secrets while retaining oauth_token_secret for compatibility
## Test - git diff --check - ruby YAML parse for prow-jobs/pingcap-inc/tiflow/release-presubmits.yaml and prow-jobs/pingcap-inc/ticdc/release-presubmits.yaml (commit: a537d31)