Process images with Sharp in external markdown content

[laurenskling]

I'm processing markdown fetched via gatsby-source-graphql as this example:
https://github.com/gatsbyjs/gatsby/blob/master/examples/using-gatsby-source-graphql/gatsby-node.js#L51

My Markdown contains images, and I would actually like to process them with sharp, to create optimized images. Like gatsby-remark-images can do. Any thoughts of how to achieve this?