Create a GL classification, typically for a value from your ERP. A classification is identified by its type,
thirdPartyId and vendorValueId. Creating an identical classification again returns the existing one with
status 200. Creating one with the same type, thirdPartyId and vendorValueId but a different payload
returns 409. Use :find and then update the existing classification instead.

Every id in glEntityIds must be an existing GL entity. An empty glEntityIds applies the classification to
the whole organization, which principals restricted to specific entities are not allowed to do.