Mandatory API parameters shouldn't be called 'optional'

I've notice that some API endpoints list up properties as optional while there are not.

For example `POST /sidecar/configurations` lists everything as optional which doesn't make sense at all, while color is a mandatory property and the API rejects a `null` value. I don't think color should be a mandatory thing anyway, since it could do a fallback to the standard color in the graylog ui. This overall should be better documented in the swagger UI.