Create healthcheck endpoint

- [ ] GET request to route returns JSON response:
- HTTP status code
- Current datetime
- Uptime

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**WHAT:**
- an endpoint that can be used to check if the app is running

**WHY:**
- Useful for tests to ensure app is working
- Useful for future diagnostic checks and reports (ex: database connectivity status)

**HOW:**
- Example can be seen in this Express.js [article](https://betterprogramming.pub/how-to-add-a-health-check-to-your-node-js-app-5154d13b969e)