Warn in case of information loss from Unmarshal

[glooms]

Go's default json.Unmarshal disregards any information that could not be properly mapped to the provided container (struct/slice/map). If we are working with an engine version not compatible with our enigma version it is plausible we would get information loss which is dangerous in a version control or unbuild/build scenario.

We should at the very least warn the user if information loss has occurred.

[glooms]

There seems to be an easy way to do this, but it has a couple of key limitations that might make it poorly suited for our case.

Using the builtin Decoder from encoding/json you can set DisallowUnknownFields() which will cause the decoder to return an error if there is data that is not mapped to the field of a struct. The drawback however is that it only returns the first unknown field, meaning we have no way of knowing how many such fields there are.

[glooms]

It seems like this doesn't happen as this is the same as having unrecognized fields (if I'm not mistaken).
I'll leave this open until clarification from @wennmo and @gabbaxx

[glooms]

This will only be an issue while using the --minimum flag and under the specific circumstance that corectl uses a version of enigma that was generated for a QIX-api version older that of the engine which the user is using.

We could raise a warning, if this is the case.