[FRONTEND] Connect the policy to sanity

[bcho892]

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

Right now policy is hard-coded, we should make a schema that uses https://www.sanity.io/docs/block-type

Refer to https://github.com/UoaWDCC/uasc-web/wiki/Sanity-Studio-Development

We need the following sections:

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