Make player configuration mutable

[defagos]

As a developer integrating Pillarbox I would like to be able to provide a setting for skip intervals, without having to recreate a player to have them applied, which is not acceptable if the user is playing content.

Acceptance criteria

• The player configuration is mutable.

Tasks

• Make configuration mutable.
• Remove configuration from initializer.
• Ensure mutations are correctly applied internally (e.g. enabling/disabling external playback).
• Make sure the following is now possible in the demo:
  • Start video playback with some skip intervals set.
  • Enter PiP.
  • Update skip intervals in the demo app settings.
  • Restore from PiP. The skip intervals should have been updated.