[Home Page] Add Partners section

[samderanova]

As with last year's site, we'll want to set up a Partners page to showcase the organizations that are hosting workshops, mainly UCI ones.

• [ ] Create a new schema for partners
• [ ] Obtain and upload images to Sanity
• [ ] Add the new partners section on the home page, below the sponsors section.

Since this project involves Sanity, make sure to add the sanity label when opening the PR for this issue.