feat: Introduce new database schema for DatabaseSessionService

Part 1 of #3605.

This change adds a new schema that uses JSON serialization to store Events data in the database. A new "adk_internal_metadata" table is also added to store information like schema version. Since we want to keep supporting existing DB, we fork from the original schema and call it "v0", while the new one is called "v1".

The change is no-op for existing users. In later change, the new schema will be used for new databases, and migration scripts will be provided for existing databases.

Co-authored-by: Liang Wu <wuliang@google.com>
PiperOrigin-RevId: 844986248

Author: wuliang229