[BUG] Generate manifest api schema inconsistency for services

Issue

Generate manifest schema inconsistency for services

Context

On call to "/v3/apps/$GUID/manifest" api returns the services as array of strings when expected was array of objects.
This inconsistency creates problem for strongly typed clients.

Steps to Reproduce

cf push

applications:
- name: http-bin
  docker:
    image: kennethreitz/httpbin
  services:
  - name: xsuaa-tf
  processes:
  - type: web
    disk_quota: 1024M
    health-check-type: http
    health-check-http-endpoint: /get
    instances: 1
    memory: 256M
    readiness-health-check-type: http
    readiness-health-check-http-endpoint: /get

export GUID=$(cf app http-bin --guid)
cf curl "/v3/apps/$GUID/manifest"

---
applications:
- name: http-bin
  docker:
    image: kennethreitz/httpbin
  services:
  - xsuaa-tf
  processes:
  - type: web
    instances: 1
    memory: 256M
    disk_quota: 1024M
    log-rate-limit-per-second: -1
    health-check-type: http
    health-check-http-endpoint: "/get"
    readiness-health-check-type: http
    readiness-health-check-http-endpoint: "/get"

Expected result

I would expect the returned schema to have services as

  services:
  - name: xsuaa-tf

Current result

Currently we are getting array of strings even when we are pushing it as an array of objects.

Reproduce the inconsistency with cf push and cf curl "/v3/apps/$GUID/manifest" using the manifest in the issue. Trace the /v3/apps/$GUID/manifest response handling and related schema or serialization code; done means services are returned as objects with a name field rather than strings, with coverage for this case.