Implement health package

[juliaogris]

• Define Heath gRPC service and protos.
• Add tooling and docs for protoc code generation.
• Implement Health gRPC and HTTP Servers.
• Document carefully for public godocs..

Package docs

Package health contains a gRPC and an HTTP server providing application health related information.

Applications may use this package to provide liveness and readiness endpoints for Kubernetes probes.

Application version information is also made available which should be set at build time with the -X linker flag. This helps identify exactly which version of the application is healthy or not.