Enable streaming through the APIServer

[logan-markewich]

Implement the equivalent of what we have in workflows:

handler = workflow.run()
async for event in handler.stream_events():
    # do something with event
    pass

for Llama Deploy through the API Server, something like GET http://apiserver.local/my-deployment/events

Sub Tasks

• Add endpoint to API Server deployments resource to get event stream using client's get_task_result_stream method. #296
• Modify WorkflowService.process_call() so that it knows to wait for manually produced Events (e.g., once it sees a InputRequiredEvent it knows it needs to wait for a HumanResponseEvent) #297
• Add send_event method to SessionClient (to enable a user to do the equivalent of ctx.send_event(ev)) #298
• Add API Server endpoint to be able to send event to a WorkflowService using SessionClient.send_event #300