Better `FieldPath` argument validation

[cvauclair]

Is your feature request related to a problem? Please describe. Yes. When constructing FieldPaths with arguments, any extra arguments (i.e.: arguments which don't exist in the subgraph schema) are silently ignored, leading to harder debugging in case of errors like typos.

Moreover, although the values of real arguments are type-checked, the exceptions are cryptic and uninformative.

Describe the solution you'd like When constructing FieldPaths with arguments, for each argument, Subgrounds should check whether:

1. The argument exists in the schema
2. The type of the argument's value matches the type indicated in the schema
3. If using relative FieldPaths (e.g.: subgraph.Query.entities(orderBy=subgraph.Entity.field)), validate that the field type on which that argument is applied matches the type of the relative FieldPath (i.e.: the type of entities matches the Entity object).

Error messages should also be clear and informative. E.g.: "X is not a valid value for argument orderBy".

Describe alternatives you've considered None

Additional context None

Implementation checklist

• [ ] Validate arguments
  • [ ] Check whether the argument exists in the schema
  • [ ] Check whether the value given to the argument matches the type specified in the schema
  • [ ] Check whether relative FieldPaths match the type of the field
• [ ] Improved error messages