[FR] Add service_instances and service_bindings endpoints

[kanngiesser]

Is your feature request related to a problem? Please describe.

The Broker does not yet implement the GET /v2/service_instances/:instance_id and GET /v2/service_instances/:instance_id/service_bindings/:binding_id endpoints which are specified for the Open Service Broker API.

Currently it is not possible to fetch (user-) parameters which were sent for provision and bind request respectively; Provision and bind parameters cannot be fetched from the service broker and, hence, cannot be retrieved from the Cloud Controller / CF-API, as well. Once provisioning or binding succeeded, parameters are neither available to platform maintainers nor to platform users (unless they saved the parameters in some other place).

We found provision and bind parameters to be a valuable resource to support platform users in utilizing service offerings and for debugging; Without parameters it is nearly impossible to figure out, what users actually did and why their service instance or credential might not work as expected.

Implementing this feature should allow to fetch provision and bind parameters directly from the service broker as well as from the CF-API (v3/service_credential_bindings/:binding_id/parameters")

Describe the solution you'd like

The Broker should implement both endpoints according to the OSB-API specification. The service catalog should return the property "instances_retrievable": true for all service offerings and "bindings_retrievable": true for all offerings which are bindable.

Required changes for both endpoints, the service catalog and tests are implemented in this MR: #1139

Describe alternatives you've considered

Additional Context

Priority
Medium

Priority Context

Platform

Applicable Services
Applies to all service offerings

[blgm]

Implemented in #1139 and released in https://github.com/cloudfoundry/cloud-service-broker/releases/tag/v2.5.0