Media player-Allow automations on actions

**Describe the problem you have/What new integration you would like**

When a media player action is issued, such as media_player.play, media_player.pause, etc. besides performing the action, be able to perform an automation with it, such as turning on a GPIO pin to switch on an amplifier, or send a signal to switch the source on the receiver.
**Please describe your use case for this integration and alternatives you've tried:**

Right now it works if the ESP is in a self-contained unit, and as long as the speaker is always connected and the amplifier is always on. If the ESP is part of a bigger media player system, there's no way of controlling the system directly from the ESP based on the action.
**Additional context**

The system could maybe be controlled with an automation from HA, but it would be nice if the ESP could be the controller.

Start by tracing the media_player.play and media_player.pause actions and how GPIO control is represented on the ESP. The issue names no files or tests, so first determine where media-player actions and automations meet. Done would let a media-player action trigger the requested external amplifier or receiver control without relying on a separate Home Assistant automation.

Written by the indexing model from the issue text.