Confusing non-symmetry of data structure for System/inputs GET and POST

I want to create an HTTP input via curl to automate the setup of the graylog server.

System/inputs GET returns a structure with a property `attributes` for an input.
System/inputs POST however expects a property `configuration`.

I would expect to be able to use the structure returned by GET as a sample to create an input mechanically. I had to rename `attributes` to `configuration`. The input was created ok.

This is confusing. A REST resource should look the same for POST and GET.

## Expected Behavior

## Current Behavior

## Possible Solution

## Steps to Reproduce (for bugs)

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## Context

## Your Environment

* Graylog Version: 2.2.2
* Elasticsearch Version:
* MongoDB Version:
* Operating System:
* Browser version: