psd2 catalogue should cause spelling=ISO20022 header to be sent

[simonredfern]

psd2 catalogue should cause spelling=ISO20022 header to be sent with API call requests
i.e.
https://apiexplorersandbox.openbankproject.com/?version=2.0.0&psd2=true
should cause the APIs to show ISO20022 spelling of fields.

[constantine2nd]

@simonredfern Ready for testing.