Starts an agent call.
Agent must be active and use an active LLM, and channel must support agent calls, i.e. support AI agents.
By default, calls bypass quiet hours restrictions and will be made immediately. Set bypass_quiet_hours to false
to respect quiet hours restrictions (weekdays 10 PM - 7 AM, no calls on weekends) and business hours, which are
calculated using the channel's timezone (defaults to "America/Los_Angeles"). When restrictions apply, calls are
automatically scheduled for the next available time. But attention, since we are introducing a new behavior,
we default it bypassing these restrictions in order to not disrupt existing workflows, but the default behavior
will be soon changed to applying these restrictions unless bypass_quiet_hours is set to true.