Allow optimizing for format, but not size

[Cretezy]

We have images which we don't care about optimizing in size, however generating in better formats (Like AVIF) is important to us.

Does it make sense to add to this plugin? I can contribute a PR.

[marlokessler]

Hi @Cretezy, this seems like a valid use case. It would be awesome if you could contribute the feature as a PR.

I think the best way to do this is by allowing image size objects without a width or height where only the new formats are then generated, e.g.:

sizes: [
    {
      name: "original",
    },
]

What do you think?