chore(showcase):added problem.studio to sites.yml (#21163)
chore(showcase):added problem.studio to sites.yml (#21163)

* New submissions for site showcase

* removed source_url and added url to other site

* Update sites.yml

* added problem.studio

* Update docs/sites.yml

Co-Authored-By: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>

* Update docs/sites.yml

Co-Authored-By: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>

* Update docs/sites.yml

Co-Authored-By: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>

Co-authored-by: Michal Piechowiak <9f3259e2eef1b9102300663eaa080e26c8e9c01f@gmail.com>
Co-authored-by: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>
Co-authored-by: Obinna Ekwuno  <25b3cf641f4285fe22bc76bbc2c5bf06c5083ede@gmail.com>
Co-authored-by: GatsbyJS Bot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>

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