fix(gatsby-plugin-utils): Export two IRemoteFile utility types

[LekoArts]

Description

When one wants to create nodes (either for Image CDN file or image) and use TypeScript to assert the shape of the NodeInput object, one was at a loss since no types for that were exported.

With this PR you then can use it like this:

import type { IRemoteImageNodeInput } from "gatsby-plugin-utils"

const assetNode: IRemoteImageNodeInput = {
  id,
  url: data.url,
  mimeType: `image/jpg`,
  filename: data.url,
  width: data.width,
  height: data.height,
  placeholderUrl: `${data.url}?w=%width%&h=%height%`,
  alt: data.alt,
  parent: null,
  children: [],
  internal: {
    type: NODE_TYPES.Asset,
    contentDigest: gatsbyApi.createContentDigest(data),
  },
}