Health check endpoint

[benCoomes]

The azure function app hosting Equipper backend was deleted sometime in Nov-Dev 2023. I didn't notice for a while. No alerts fired, even though every API request resulted in a 503 response. Re-uploading the app fixed the problem, but it shouldn't have taken so longer to detect the issue.

Equipper should have a health check endpoint that can be called to verify:

1. The API is live
2. Strava connection is healthy
3. Database connection is healthy

If any of these are unhealthy, a non-200 response should be returned.

Then an alert should be set up in azure to check this endpoint periodically and fire an alert if it is not a 200 response.