fix(firestore-bigquery-export): Add Backward Compatibility and New Event Types for Firestore BigQuery Export

[Gustolandia]

#1981

Description (issue 1981):
This PR introduces backward-compatible event types while adding new naming conventions for Firestore BigQuery Export. The changes ensure robust event handling across multiple versions of the extension. The following updates have been made:

Key Changes:
1. New Event Types:
• Introduced new events using the updated naming convention:
• firebase.extensions.firestore-bigquery-export.v1.onStart
• firebase.extensions.firestore-bigquery-export.v1.onSuccess
• firebase.extensions.firestore-bigquery-export.v1.onError
• firebase.extensions.firestore-bigquery-export.v1.onCompletion
2. Backward Compatibility:
• Maintains the existing events under the old naming convention:
• firebase.extensions.firestore-counter.v1.*
• Both old and new event types are published for each operation to ensure smooth migration.
3. Refactored Event Publishing:
• Updated event publishing logic to dynamically handle both old and new event types.
• Functions now publish events using Promise.all for better concurrency.
4. Unit Tests:
• Enhanced unit tests to verify:
• Events for both old and new naming conventions are correctly published.
• Proper handling of CREATE, DELETE, and UPDATE scenarios.
• Mocked Eventarc interactions for improved testing reliability.
5. Code Improvements:
• Refactored events.ts to dynamically generate both old and new event types for reuse.
• Added extensive documentation to clarify the event publishing logic and backward compatibility strategy.

Testing:
1.	Unit Tests:
•	Added test cases for CREATE, DELETE, and UPDATE scenarios.
•	Verified that both old (firestore-counter) and new (firestore-bigquery-export) event types are published.
2.	Local Testing:
•	Tested event publishing with mocked Eventarc to ensure consistency.
•	Verified performance and reliability with simulated Firestore data changes.

Checklist:
•	Code refactored for event compatibility.
•	Tests updated and passed successfully.
•	Documentation updated for event naming conventions.
•	Verified performance under high-load scenarios.

Notes:
•	This PR ensures compatibility while transitioning to the new naming convention.
•	Developers can gradually update their consumers to listen for new events.
•	Legacy systems will remain unaffected by these changes.

[Gustolandia]

@cabljac Do you have any final comments regarding this?

Changes applied in the last ammend