[Feature] add header for download image

[beerline]

Hi, and thank u for such a good library!

In my case image on server protected by auth token which should be passed in the Header.
Since blurhash used Image.network under the hood now it is impossible to pass token.

Seems like to reach this goal at the BlurHashState.prepareDisplayedImage instead of Image.network we need use:

Image(
    image: NetworkImage(
    imagePath,
    headers: {
      HttpHeaders.authorizationHeader: 'token',
    },
),

Let me know what u thinking and i can help with implementation

[Robert-Scub]

Oh this is an interesting case!
We should be able to pass an optional Headers paramaters.
Would it be enough for you?

[Solido]

Pushed on 0.6.6 @beerline