Fix BigQuery ingestion errors and improve Cloud Build robustness

[Mahalaxmibejugam]

This PR fixes BigQuery ingestion failures caused by schema shifts and improves the robustness of the Cloud Build pipelines.

Key Changes:

• BigQuery Ingestion: Refactored ingest.sql to use dynamic SQL with explicit, alphabetically ordered column lists. This prevents type/count mismatches when schema evolves.
• Fail-Fast Validations: Added checks for required substitution variables in both benchmarks and ingestion pipelines to prevent wasted resources.
• Cleanup Fallback: Added TTLs (1h/4h) to OS Login SSH keys in E2E and benchmarks pipelines as a safety fallback.
• Bug Fix: Fixed a bug in benchmarks-cloudbuild.yaml that added a trailing hyphen to sanitized branch names (e.g., main-).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.50%. Comparing base (b1fee12) to head (b60efd0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #849   +/-   ##
=======================================
  Coverage   88.50%   88.50%           
=======================================
  Files          15       15           
  Lines        2993     2993           
=======================================
  Hits         2649     2649           
  Misses        344      344           

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