Add challenge 3 of 100DaysOfGatsby (#20584)
Add challenge 3 of 100DaysOfGatsby (#20584)

* Add challenge 3 of 100DaysOfGatsby

* chore: format

* Update docs/blog/100days/gatsby-image/index.md

Co-Authored-By: LB <barth.laurie@gmail.com>

* Update docs/blog/100days/gatsby-image/index.md

Co-Authored-By: LB <barth.laurie@gmail.com>

* chore: format

Co-authored-by: GatsbyJS Bot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>
Co-authored-by: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>

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