feat: Health check methods

[willhausman]

#302

These are methods that can be used for checking health. I did not explicitly add an endpoint because the format of returning health checks varies slightly. These are methods that can be called with a custom implementation or using another package, e.g. terminus or lightship.

[paveltiunov]

@willhausman Looks good to me! Also agree on endpoint. Would be nice to have it in the docs though as it may not seem obvious on how to add this health check route.

[hemanthsj]

Thank you @willhausman