Add native param support to mediaTypes

[matthewlane]

Type of change

• Feature

Description of change

This PR allows specifying requested native assets in the new mediaTypes ad unit parameter object. This can currently be done with the nativeParams ad unit object, and that continues to work. All values that work in nativeParams may now be specified in mediaTypes.native

mediaTypes: {
  native: {
    title: {required: true},
    sponsoredBy: {required: true},
  }
}

is equivalent to

mediaType: 'native',
nativeParams: {
  title: {required: true},
  sponsoredBy: {required: true},
}

the image type also works in the new mediaTypes form

mediaTypes: {
  native: {
    type: 'image',
  }
}

[mkendall07]

deepAccess FTW