Update health check if database connection drops

[wadeking98]

Issue:

Currently issuer-kit api contains a health check to determine in the initial connection to the database succeeds. However, if the initial connection succeeds and then the database comes offline later, the health check still returns 200 even though the api is no longer connected to the db.

Requested Change:

Update the /health endpoint to respond with 503 if the database is currently disconnected and 200 if the database is currently connected to the api