Extendable backend using plugins

[mgineer85]

Currently working on a plugin mechanism that allows flexible extension of the backend. It could be used to modify the apps behaviour by attaching functions to events. Example: WLED integration or GPIO could be moved to the plugins and so customized. Add a function to switch a GPIO when the photobooth starts a countdown would be very simple to realize...

The implementation is currently here and will be merged later once the basic functionality is ready: https://github.com/photobooth-app/photobooth-app/tree/plugin-architecture

Functions planned:

• Discover plugins by entry-point (this way the community could write plugins and they are detected automatically if installed by others)
• Register class detected by entry-point and initialize.
• Start / Stop plugins as the app starts/stops
• Automatically detect if the plugin has configuration options and show the options in the frontend.
• Define hooks
  • plugin start/stop
  • config save/load/persist
  • statemachine countdown, shoot, standby, ...
  • acquisition trigger, captured, ...
  • mediaprocessing pipelines
  • ...?
• Create example plugins
  • WLED
  • GPIO output
  • custom commands plugin
• Add documentation
  • How to write a plugin
  • How to publish a plugin
• add tests
• error handling to avoid plugins breaking the whole app if they fail.

Out of scope currently

• extending the frontend