Add Endpoint serverLogicSuccessPure and serverLogicErrorPure

[geirolz]

This PR adds two methods to Endpoint to avoid boilerplates

• serverLogicSuccessPure - For cases where the result is always a pure success ( healthcheck, stream*, etc... )
• serverLogicErrorPure - For cases where the result is always a pure failure

* stream = when you build a streamed API the logic is F[Either[E, Stream[...]]] since the errors and the side effects will be handled by the stream you often have to write .serverLogicSuccess(i => myStream(i).pure[F]). with serverLogicSuccessPure you can avoid that small boiler plate when needed.

I also wonder if it would be useful to add something like serverStreamLogic which is equals to serverLogicSuccessPure but have the constraints that the output is a stream ( Idk if this is feasible ). The advantages in this case are just the readability and the clarity of the code

[adamw]

Thanks! I think the streaming variatns might be too specialised, as they would also assume that the stream is the only output