Add flag to change healthcheck url

[kdauzickas]

Health check urls aren't really standardized - many use healthz but just as many use completely custom endpoints.
Having a command line option to change this url adds some flexibility when deploying this application without provided helm chart.

[jacobbednarz]

Thanks for the contribution @kdauzickas! Would you be able to update your Pull Request description with a little context about this change? On the surface, it looks fine however I'd like to ensure I'm fully understanding your issue and the intended fix.

With this change, we'll also need to look at updating the README command line options section as well to keep these documented.

[jacobbednarz]

Appreciate the update here @kdauzickas and apologies on the delay. As you force pushed this, I didn't get a notification the change was ready. This looks fine to me! Thanks again 🍰