Enhancement: Support more types of media files

[estruyf]

This feature is required for the preparations of the upcoming file field type. #308

By default, the media dashboard should support image, video, and audio files.

Mime types:

• images/*
• video/*
• audio/*

Configurable from the frontMatter.media.supportedMimeTypes setting.

"frontMatter.media.supportedMimeTypes": [
  "image/*",
  "video/*",
  "audio/*"
]