Agent states management improvements

[jlia0]

The agent states is very useful, however there are a few improvements needed.

1. Use fast-json-patch to sync states instead of sending the entire state via websocket
2. Add selective state sync to the client-side, to avoid sharing sensitive state data
3. Add a persist flag to store states into the SQL table, to avoid frequent data write operations when updating states

With the above improvements, I can essentially use the state to store the chat messages on the backend, and send over selective messages to the client-side, while achieving good performance.

[lmaccherone]

I like this concept, but I recommend it use RFC-7396 JSON Merge Patch rather than RFC-6902 JSON Patch that fast-json-patch implements for several reasons:

1. JSON Merge Patch is simplier
2. More efficient with bandwidth
3. Most importantly, SQLite has built-in support for it and DO's storage engine is built on it.

The system I'm building right now uses it so I did my research before choosing it.