As a Korifi API user I want to be able to get service offering fields when listing service instances

[danail-branekov]

GIVEN I have enabled the experimental managed services flag in the helm values
WHEN I have created service brokers
WHEN I /v3/service_instances?fields[service_plan.service_offering]=guid,name,relationships.service_broker
THEN I see the guids, names and broker guids of the offering related to the service instance plan under included.service_offerings array, for example

{
  "included": {
    "service_offerings": [
      {
        "guid": "fc018c50-eadc-57a8-b231-fbcf147eaf78",
        "name": "xsuaa",
        "relationships": {
          "service_broker": {
            "data": {
              "guid": "813e18bc-5c9e-4b27-990f-de2f398e9ba2"
            }
          }
        }
      }
    ]
  },
  "pagination": {
  ...
  },
  "resources": [
    {
      "guid": "a07c8a84-1e85-4882-9764-fb85f57f46bd",
      "name": "my-service-instance",
      ...
  ]
}

Dev notes:

• Managed services proposal
• List service instances docs
• Fields concept docs