As a Korifi API user I want to be able to get service broker 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.service_broker]=guid,name
THEN I see the guids and names of the brokers providing the result service instances under included.service_brokers array, for example

{
  "included": {
    "service_brokers": [
      {
        "guid": "813e18bc-5c9e-4b27-990f-de2f398e9ba2",
        "name": "btp-sm"
      }
    ]
  },
  "pagination": {
  ...
  },
  "resources": [
    {
      "guid": "a07c8a84-1e85-4882-9764-fb85f57f46bd",
      "name": "my-service-instance",
      ...
  ]
}

Dev notes:

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