Can't use backend without mongo url env secret

[ptruong0]

Description

Check for mongo env variable in app.ts. Also added some error handling on the backend to handle failed requests to roadmap, reviews, etc routes

Search, course, and professor pages should work as usual. Roadmaps can be saved locally but not to the user account.

Screenshots

Steps to verify/test this change:

• Verify changes work as expected on staging instance

Final Checks:

• Verify successful deployment

(optional)

• Write tests
• Write documentation

Issues

Closes #446

[js0mmer]

I'm getting these errors when running locally with the example env file. Doesn't seem related to Mongo but it still prevents users from running without secrets.

I've suggested some conditions that should fix this