[gatsby-plugin-sharp] option not to add original image

[VladyslavBondarenko]

Please, make this optional.

I need only specific sizes webp from original png or jpg images and I don't need to link the original image. I'd expect to have images only based on breakpoints and maxWidth, but webp with original size is generated too.
I can easily filter srcSet not to use the big image, but my issue is different. I want to make the building process faster and the generation of an extra image for each image takes quite a time because I have over 3k images.