Added import for pgConfig.
Added a postgresClient property to the Siddi class.
Added the initPostgres method to initialize the Postgres connection.
Called this.initPostgres() in the constructor.
Added the close method to properly close the Postgres connection.

These changes add Postgres support to the Siddi class while maintaining the original functionality and code structure. The new methods (initPostgres and close) are documented in the same style as the existing methods.

- Integrate Postgres as a new event consumer
- Add pgConfig.ts for Postgres connection configuration
- Modify siddi.ts:
  - Add postgresClient property
  - Implement initPostgres method for connection setup
  - Update close method to handle Postgres connection
- Update consumers.ts:
  - Add Postgres consumer with test, identify, and track methods
  - Implement robust connection testing for Postgres
- Ensure backward compatibility with existing consumers
- Add necessary type declarations for global Postgres client

This commit enables Siddi to store events and user data in a Postgres
database while maintaining support for existing event consumers.