health: Health check API

[tonybase]

implement is based on gRPC health check API： https://github.com/grpc/grpc/blob/master/src/proto/grpc/health/v1/health.proto

Health Status:

• UNKNOWN
• SERVING
• NOT_SERVING
• SERVICE_UNKNOWN

There should be a health package in kratos for HTTP/gRPC health check, the status should be set to NOT_SERVING on application exit.

type Health interface {
    SetStatus(ServingStatus)
}

health check API in HTTP：

GET /health/check?service=

{
    "status": "SERVING",
}