Add regions to kafka

[Goyo (korgan00)]

Multi-Region Event Streams Routing

Summary

Implement region-aware event publishing for Qiskit Functions. The service is global but usage events must be published to regional Kafka buses. This change makes KafkaEventStreamsClient hold multiple regional producers and route each job's usage events to the correct bus based on the region encoded in the job's instance CRN.

Details and comments

Core

• kafka_event_streams_client.py: Changed from single producer to registry of regional producers. Auto-discovers regions from EVENT_STREAMS_BOOTSTRAP_SERVERS_<REGION> env vars. Routes events by extracting region from CRN (6th colon-delimited segment).

Tests (9 new cases)

• Default region from unsuffixed vars (back-compat)
• Suffixed vars discovered by scan
• EVENT_STREAMS_DEFAULT_REGION respected
• Correct producer selected by region
• Unconfigured region raises error
• Null/malformed CRN falls back to default
• Missing API key raises at init
• Startup log lists regions

Environment:

EVENT_STREAMS_ENABLED=true
EVENT_STREAMS_DEFAULT_REGION=us-east
ENVIRONMENT=production

Checklist

• I have added tests to cover my changes.
• I have updated the documentation accordingly.
• I have added a release note for any user-facing change (new feature, bug fix, deprecation, or breaking change), or this PR has no user-facing changes.