[Major] Add server-side input validation

Install zod 1 for use in input parsing/validation. Bump validator, which we use in conjunction with zod. We remove the custom sanitizeQuery function.

Some functional fixes discovered while validating/parsing input:

The requireLogIn middleware handles the case where req.session.user is not set (due to express session requiring HTTPS). It falls back to re-logging in the user through the session token.
The requireLogIn middleware now passes req instead of req.cookies.session_token to the logInBySessionToken. Previously, this would have been a runtime error.
Make express-session use the secure option in production but not in dev. #185 tracks being able to use HTTPS in dev and tests.
We forego calling nodemailer's sendMail function in tests and dev environments to avoid incurring costs from our email provider, Mailgun.
When requesting search results, the front end would send Infinity, which serializes to undefined over the wire. We now send 50 instead.
Add a VS Code launch command for debugging server-side tests without timing out.

dchege711 / study_buddy

[Major] Add server-side input validation #182