Usage reporting plugin needs to support input fields

[dylan-partly]

Usage reporting seems very incomplete without knowing the usage of input fields.

The variable reporting is insufficient for the use case of checking apollo studio to see whether a deprecated input field is still being used, so it can be removed. This is because you can hard code values into a graphql query (not input them as variables) and the sendVariableValues will not report these values.

There is this merge request that was reverted and never reintroduced for some reason #4654 (cc @sachindshinde)