Is your feature request related to a problem? Please describe.

• not a problem, feature to add missing functionality

Describe the solution you'd like
In my PR that I opening I implemented a endpoint and handler that follows what the Python ADK and ADK docs do for Updating (patching) a Session's state. This process updates the Session, and works in-memory and in database servies.

Describe alternatives you've considered

• no alternatives, we need to implement this to mimic Python ADK.

Additional context
I have this completed. Opening PR in a few minutes 🚀 🐶