Suggestion: Allow handle program to initiate conversations

[Shulyaka]

Currently the pipeline only starts the handle program after user speech. However there are use cases such as:

1. Setting up a reminder
2. Timer
3. Multiple responses from the handle program for a single request, such as "doing it now, please hold on...", then "Done."

I suggest two options:

1. Start the handle program in advance and keep it running
2. Add a new domain (i.e. agent) that is able to initiate conversations on behalf of the user, but I am not sure about the communication protocol.