Better `FieldPath` argument validation

**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

*Originally from: cvauclair*

Look at the FieldPath class and its argument handling. The subgraph schema is used for validation. Start by understanding how arguments are currently passed and ignored. Check the schema for argument definitions and types. Write validation logic that raises clear error messages for missing arguments or type mismatches. Test with a subgraph query to ensure errors are informative.

Scritto dal modello di indicizzazione a partire dal testo della issue.