Fleet package_policy API use deprecated property policy_id

## Description 

Related PR for fleet https://github.com/elastic/kibana/pull/184636

Fleet has introduced a change that allow a package policy to belong to multiple agent policy, for this the property `policy_id` has been deprecated in favor of the new `policy_ids` one in both request and response of the fleet `package_policies` API.

This should be changed before the property is removed. 