Track feature use and notify users about features they haven't tried yet

[spencerckhuang]

*** TODO: Please fill out all below TODOs and testing checks below before making a pull request! Skip/delete sections at your own discretion. ***

📝 Summary

*** TODO ***

🔍 Change Log

*** TODO (a list of any major/significant files changed is sufficient) ***

⚠️ Base Testing

Please fill in the following required testing steps with a checkbox (✅) before making this PR, or indicate why they are not necessary for this change:

[ ] docker-compose build && docker-compose up and the https://jhu.sem.ly endpoint works successfully

[ ] Semesterly CI successful

[ ] Backend linter successful

[ ] TSLint successful

🧪 Other Testing Steps

*** TODO: List any other testing steps taken for this PR ***

💻 Local Testing Instructions

*** TODO: Include any other necessary instructions for local testing ***

To test locally from a forked repo, run:

git fetch https://github.com/<username>/<fork-repo>.git <branch-name>:pr-<PR_NUMBER> && git checkout pr-<PR_NUMBER>

Please contact the owner of the fork in case the fork's branches are not publically accessible.