Add voice assistant config

[gnumpi]

Part of #55 (Adding the configs for the voice assistant pipeline)

• add voice_assistant component itself to the config
• introduce a 'timer.yaml' which contains the timer configuration, which is provided by the voice_assistant component
• adjust buttons and global state variables to align with voice_assistant config of LED animations working, music streaming working if song is playing at… #55
• add voice assistant media files to media_player