support for K8S svcat service instance updates

[gberche-orange]

Expected behavior

• As a osb service provider
• In order to support service instance updates from K8S svcat
• I need osb-cmdb to support K8S-flavored PATCH /v2/service_instances/:instance_id requests with missing plan_id without errors

Request Field	Type	Description
plan_id	string	If present, MUST be the ID of a Service Plan from the Service Offering that has been requested. If this field is not present in the request message, then the Service Broker MUST NOT change the Service Plan of the Service Instance as a result of this request.

Observed behavior

Osb-cmdb rejects the request with Invalid plan received with unknown id: null

CloudFoundry seems to systematically provide plan_id while k8S svcat only provides it when it changes.

Osb-cmdb does not really need the plan_id to update a brokered service instance:

• backend service instance is identified by:
  • org-name (derived from osb-cmdb tenant)
  • space-name (i.e. brokered service definition name)
  • service-instance-name (i.e. brokered service instance guid)

Currently, the plan_id is abusively required by osb-cmdb due to:

• excessive input validation during update https://github.com/orange-cloudfoundry/osb-cmdb/blob/1c62877fc1b63de3f34934422d83a2756f439085/osb-cmdb/src/main/java/com/orange/oss/osbcmdb/serviceinstance/OsbCmdbServiceInstance.java#L478-L479
• fetch backingServicePlanId in the case of a plan upgrade: should support missing brokeredPlan Id|Name and return null update-requested backend plan id https://github.com/orange-cloudfoundry/osb-cmdb/blob/1c62877fc1b63de3f34934422d83a2756f439085/osb-cmdb/src/main/java/com/orange/oss/osbcmdb/serviceinstance/OsbCmdbServiceInstance.java#L500
• pass update-requested backend plan id to CF API: supports null value when plan does not change:

Affected release

Reproduced on version v1.4.0 and earlier