Remove manual requests

[nponsard]

Currently some functionalities are implemented with custom functions because the generated code doesn't handle the request correctly.

The last issue holding back these changes is the serialization of application/x-pem-file format. openapi-json-schema-tools/openapi-json-schema-generator#244

Linked issue : https://git.nitrokey.com/nitrokey/nethsm/nethsm/-/issues/246