[BACKEND] Annotate UserAdditionalInfo model

[choden-dev]

Is your feature request related to a problem? Please describe.
We should annotate our DTOs (data transfer object) so that they can be validated.

Describe the solution you'd like

Check out the examples at https://tsoa-community.github.io/docs/annotations.html and look at the firebase architecture page

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

BEFORE MERGING

• Integration test written for services
• Code generation run (hint: yarn workspace server tsoa spec-and-routes)
• Schemas annotated if adding new models
• Appropriate mocks created where possible
• 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