Save the AI assistant settings

Multipart: data (JSON with any of display_name, avatar_type [default|initials|image], personality, response_length, language [auto|en|es|ca|fr|it|de|pt|ru|ja|zhchs|zhcht], voice_enabled, voice_auto_send, voice_silence_ms [1000-6000], remove_avatar) and optionally avatar (PNG, JPEG or WebP up to 2 MB). With avatar_type=image an image must exist or come in the request.