Error when "details" error field is populated in network/options response

Hi!

An error is thrown at line 202 in `asserter/network.go` when an error from the network/options endpoint response has the `details` field populated.

This looks like desired behavior, I'm just not sure why, because according to the [documentation's response example](https://www.rosetta-api.org/docs/NetworkApi.html#200---ok-1) for this endpoint the an entry in the allow.errors array can have this property populated. This is also sustained by the documentation for the [Error](https://www.rosetta-api.org/docs/models/Error.html) type, present in the [Allow](https://www.rosetta-api.org/docs/models/Allow.html) type.

Is this a case of documentation that needs to be updated, or am I misunderstanding something?

Read asserter/network.go at line 202, then compare its handling of a populated details field with the linked NetworkApi, Error, and Allow documentation. Determine whether the endpoint response is being rejected incorrectly or the documentation is inaccurate; done means the behavior and documented response contract agree.

Written by the indexing model from the issue text.