Fix Deployment model definition

[mattt]

#258 added fields to the Deployment model provided by the new deployments.{get,list,update} endpoints. However, those were implemented against a version of the OpenAPI specification that disagreed with the actual API responses. Specifically, the min_instances and max_instances properties were listed as subproperties of a scaling object rather than direct fields. The result — as reported in #270 — was Pydantic validation errors like this:

raise validation_error
pydantic.v1.error_wrappers.ValidationError: 1 validation error for Deployment
current_release -> configuration -> scaling
field required (type=value_error.missing)"

This PR updates the Deployment model to correctly locate min_instances and max_instances as properties of current_release.configuration.