Add support for propery source origin introduced in boot 2

[spencergibb]

This would be helpful in debugging configuration problems.

@dsyer @twicksell

[spencergibb]

Boot's env endpoint changed for a simple key -> value, to key -> {value, origin}. Config server would need to be backward compatible. Two options, either a new prefix (v2) or a content type (which is what boot uses). I think I lean towards the content type.

Boot's content type application/vnd.spring-boot.actuator.v2+json, so I would propose application/vnd.spring-cloud.config-server.v2+json.

Example output:

{
  "name": "foo",
  "profiles": [
    "default"
  ],
  "label": null,
  "version": "a611374438e75aa1b9808908c57833480944e1a8",
  "state": null,
  "propertySources": [
    {
      "name": "https://github.com/spring-cloud-samples/config-repo/foo.properties",
      "source": {
        "foo": {
          "value": "from foo props",
          "origin": "File [foo.properties]:1:6"
        },
        "democonfigclient.message": {
          "value": "hello spring io",
          "origin": "File [foo.properties]:2:27"
        }
      }
    },
    {
      "name": "https://github.com/spring-cloud-samples/config-repo/application.yml",
      "source": {
        "info.description": {
          "value": "Spring Cloud Samples",
          "origin": "File [application.yml]:2:16"
        },
        "info.url": {
          "value": "https://github.com/spring-cloud-samples",
          "origin": "File [application.yml]:3:8"
        },
        "eureka.client.serviceUrl.defaultZone": {
          "value": "http://localhost:8761/eureka/",
          "origin": "File [application.yml]:7:20"
        },
        "foo": {
          "value": "baz",
          "origin": "File [application.yml]:9:6"
        }
      }
    }
  ]
}

[spencergibb]

We could enhance the origin depending on the environment. For example, git blame information could be added, etc...

[spencergibb]

From /actuator/env

{
  "activeProfiles": [],
  "propertySources": [
    {
      "name": "configService:https://github.com/spring-cloud-samples/config-repo/foo.properties",
      "properties": {
        "foo": {
          "value": "from foo props",
          "origin": "Remote file foo.properties:1:6"
        },
        "democonfigclient.message": {
          "value": "hello spring io",
          "origin": "Remote file foo.properties:2:27"
        }
      }
    },