feat: conversational agent support

[mike-deem-uipath]

Depends on UiPath/uipath-python#1087 and UiPath/uipath-runtime-python#65 (is causing checks to fail)

Adds support for conversation agents:

• state is initialized with input messages received when the job is started. init node overwrites messages in state so that the system prompt message comes first.
• no tools are bound, the agent can just respond without invoking a tool
• only agent response messages are sent to cas (or both coded and autonomous conversational agents). CAS doesn't expect the system message and the user message is sent from the client.
• don't delete state.db if keep_state_file context option is set (the cli can set this using --keep-state-file). This allows conversational agents to accumulate conversation history across multiple runs.

[andreitava-uip]

Overall it looks ok.
Some things will need to be changed to properly support parallel execution of tools, but that's my job