Add or document livelihood/readiness endpoints for the OAuth 2.0 Auth Middleware

[stefanobaghino-da]

What is the problem you want to solve?

I would like to be able to use widely used tools (e.g. Kubernetes) to manage OAuth 2.0 Auth Middleware instances so that I can effectively achieve high availability of the service on my deployment.

What is the solution you would propose?

Add a /readyz and /livez endpoint like the HTTP JSON API Service and the Trigger Service (see https://github.com/digital-asset/daml/issues/13819).

Describe alternatives you've considered

Using another endpoint to check for the livelihood of the service, but I'm not sure about which one could be used to this end. If the problem can be solved that way, I'd find it satisfactory to document this.

[hrischuk-da]

Also, the port that the endpoint is on should be configurable so that I can combine several processes into the same Docker container but still expose each livez endpoint.

[ray-roestenburg-da]

@hrischuk-da the auth middleware service port is already configurable.