Is your feature request related to a problem? Please describe.
I'm using Google ADK to build AI agents, and my infrastructure is mostly based on Typesense for data storage and search. Currently, ADK only supports two session storage backends:

1. InMemorySessionService - Data is lost on restart
2. DatabaseSessionService - Requires a relational database (PostgreSQL, MySQL, etc.)

Since my infrastructure already uses Typesense, I'd like to use it for ADK session storage as well instead of adding a separate PostgreSQL database. This would:

• Keep my infrastructure simple and consistent
• Avoid running and maintaining an additional database
• Leverage my existing Typesense deployment

Describe the solution you'd like
Add TypesenseSessionService as a new session storage backend that uses Typesense for persistence.

Describe alternatives you've considered

1. Using DatabaseSessionService with PostgreSQL: Adds another database to maintain when I already have Typesense
2. InMemorySessionService: Loses data on restart, not suitable for production
3. External session storage adapter: Would require maintaining custom code outside of ADK