Create Firebase File model and migration file

[gavxue]

Notion ticket link

Create Firebase File Model + Migration File

Implementation description

• added FirebaseFile types
• created File sequelize model
• created migration file to generate new sql table

Steps to test

1. run these commands in backend/typescript

docker-compose exec ts-backend bash
node migrate up

2. verify that the files table is created with all appropriate columns
3. test rollback with node migrate down

What should reviewers focus on?

• model makes sense
• follows codebase patterns

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[SaqAsh]

LGTM