GET current service config

#### Feature Description

As a consul administrator, I would like a way to be able to use the CLI, or GET the api for the current configuration of a service.

Currently, unless a configuration has been added to consul via `consul config write` or the corresponding http endpoint, you cannot read it, leading to issues troubleshooting as an administrator attempting to help users debug their services.

#### Use Case(s)

1. A client is having issues with their health checks. The service registers but the health check doesn't seem to be working
2. As an operator, if I could retrieve their service configuration, and see the check I could potentially deduce what's missing or incorrect causing the health check to fire improperly.
3. A client is using the terraform module for ecs task definitions and the consul services are registering but failing in some other way
4. As these service and agent configurations are on the ECS fargate container itself, one would have to exec into the container (if this is enabled for that deployment), and locate the configs in the shared volumes and then send it to the operator/administrator.
5. If an operator/administrator/client could just do something like `consul config get -kind service -name SERVICENAME` much like service-defaults, troubleshooting would be far more streamlined and easier to handle. We could at least see if it was registering before failure, and if so, what definition its failing with.

The issue names the `consul config get` CLI command and the corresponding HTTP API, but no files or tests. Start by tracing the existing `consul config write` command and endpoint, then determine how service configuration is stored and exposed. Done means administrators can retrieve a registered service's current configuration through both requested interfaces.

Written by the indexing model from the issue text.