Add "pyatv" Python library to Homebridge Docker image
### Current Situation

Plugins that use the Python pyatv/atvremote package to provide AirPlay require connecting to the Homebridge Docker container and performing a manual install of pyatv, as Homebridge does not install it as part of the plugin. This process has to happen every time the user updates to a new the Docker image, or recreates the container.

### Proposed Change

Currently Homebridge UI shows if Homebridge, Homebridge UI, or plugins have updates. As pyatv is installed manually, there are no notifications if a new version with fixes or enhancements becomes available.

As AirPlay is a standard service in the Apple ecosystem (not HomeKit), it would be convenient if it came preinstalled by default in the docker image.

By adding one line to the Homebridge Dockerfile:
`RUN pip3 install pyatv`
the latest version of pyatv would become available when the Docker image is updated.


### Additional Context

_No response_