Outbound Phone Calling on Playground

I imagine next to the "start" conversation buttons, we can have a button with a phone icon that opens up a modal to ask if the user wants to send an outbound call to a specific phone number.

We will want the user to only call their own number (clarify the [law](https://transition.fcc.gov/cgb/policy/Telemarketing-Rules.pdf) around outbound phone in the modal).

Users can fill in their number in the configs on the left panel, or then & there in the modal itself (will be same field as datasource in the `PlaygroundContext`, etc)