Add support for user role field groups

[saleebm]

It's pretty much the same as #59 except resolved conflicts.

[saleebm]

Based on the response from this, it would be best to add it the user type as suggested.

Hey @jydmnd!

Thanks for reporting this. This ACF "location rule" is not yet supported.

For context, should anyone come across this:

The GraphQL Schema is independent of any context, such as the user's role, for example. The Schema is representation of what's possible (what can be asked for), and Resolvers take into consideration context (such as the current user, or a specific object being resolved) when resolving the info. . .but in ACF, there is context, because you're loading a specific admin page to interact with the fields.

Mapping contextual rules from ACF Field Groups, such as a specific page or a specific user role, gets tricky, because the GraphQL Schema is the same Schema regardless of resolve context
so adding support for those contextual locations has been tricky to say the least.

This is a location I think we should support.

The way I see it working would be that the fields should be added to the User Type.

This way, the fields can be asked for anytime a user is asked for. During resolution, the user role can be checked, and if the user has the assigned capability, the fields will resolve. If the user doesn't have the assigned capability, the field group will return null.