Add MQTT command to display a toast message

[bp2008]

Design and add an MQTT command to display a toast message.

Options to consider:

1. Style of toast (error, warning, info, success)
2. Toast timeout in seconds. -1 to make it permanent and give it a close button?
3. Plain text only, for security reasons.
4. Should the toast message do something on click?

• Nothing
• Maximize a camera
• Go to the Clips tab, filter by Alerts, and maximize a camera.
• Open a specific recording by ID (can this be passed an alert ID?)

5. Have an optional toast instance ID field similar to what I did with playaudio/{player_id}