out_chronicle: support the new Chronicle API #12157

Is your feature request related to a problem? Please describe.
Google SecOps is deprecating the legacy Backstory API (including the Customer Management API) and the legacy Ingestion API in favor of the Chronicle API. For details on how to migrate, see Migrate from legacy SIEM API to Chronicle API.

Key dates:

• October 26, 2026: End of sale (EOS): New instances provisioned on or after this date cannot access the legacy APIs.
• July 20, 2027: End of life (EOL): The legacy APIs shut down. Existing instances must complete migration before this date.

Currently, out_chronicle supports Backstory API only.

Describe the solution you'd like
out_chronicle support both Backstory API and Chronicle API during transition phase, then decom the legacy Backstory API.

Describe alternatives you've considered
N/A

Additional context

• https://docs.cloud.google.com/chronicle/docs/deprecations