feat: added announcement schema and create announcement page

[mio-naka]

Developer: Mio Nakagawa

Closes #33

Pull Request Summary

Completed issue #33 where I created a MongoDB announcement schema as well as the frontend for the create announcement page, along with unit testing.

Modifications

/app/createAnnouncement/page.tsx: created the frontend for the create announcement page
/database/announcementSchema.ts: created announcement schema
tests/CreateAnnouncement.test.tsx: unit testing for the create announcement page

Testing Considerations

Tested using unit testing if it renders the form correctly, updates form fields when user types, handles file selection correctly, handles form submission correctly.

Pull Request Checklist

• Code is neat, readable, and works
• Comments are appropriate
• The commit messages follows our guidelines
• The developer name is specified
• The summary is completed
• Assign reviewers

Screenshots/Screencast

[elhagen13]

Thanks for getting your issue in! Looks great!