Edit Environments API annotation

This edits the annotations for the slug parameters so that they are excluded in autogenerated grape-swagger OpenAPI documentation. The slug parameter does not exist in the documentation and is supposed to be absent as per the annotation absence: { message: "is automatically generated and cannot be changed" }. If the slug parameter is included in a request, a 400 error is sent as part of the validation. As such, it should not be included in the autogenerated OpenAPI documentation.

The OpenAPI V2 documentation will be used for dogfooding API fuzzing as per #372422 (closed) and the OpenAPI autogeneration &8926.