[FRONTEND] Set up schema for photo gallery on front end

[choden-dev]

Is your feature request related to a problem? Please describe.

We want all the content of the gallery to be changeable through a CMS rather than requiring changing the code.

Note that admins may want to display images based on:

• year
• event
• other tags

The example at https://github.com/UoaWDCC/uasc-web/wiki/Sanity-Studio-Development may be helpful

BEFORE MERGING

• Storybooks created where possible
• Tested with nock if data fetching
• Tests written for critical interactions
• PR Reviewed (For non-trivial changes)
• Changes tested after rebasing on master or merging in master (hint: git fetch origin master:master, then git rebase master or git merge master)
• All required PR checks passing