Remote Schema Permissions Validation

This module parses the GraphQL IDL (Schema Document) that's provided by the user for configuring permissions for remote schemas to a schema introspection object, which is then used to construct the remote schema for the particular role.

This module does two things essentially:

1. Checks if the given schema document is a subset of the upstream remote schema document. This is done by checking if all the objects, interfaces, unions, enums, scalars and input objects provided in the schema document exist in the upstream remote schema too. We validate the fields, directives and arguments too, wherever applicable.
2. Parse the preset directives (if any) on input object fields or argument fields. A preset directive is used to specify any preset argument on a field, it can be either a static value or session variable value. There is some validation done on preset directives. For example: - Preset directives can only be specified at ARGUMENT_DEFINITION or INPUT_FIELD_DEFINITION - A field expecting object cannot have a scalar/enum preset directive and vice versa.

If a preset directive value is a session variable (like `x-hasura-*`), then it's considered to be a session variable value. In the case, the user wants to treat the session variable value literally, they can add the static key to the preset directive to indicate that the value provided should be considered literally. For example:

`user(id: Int @preset(value: "x-hasura-user-id", static: true))

In this case `x-hasura-user-id` will be considered literally.

For validation, we use the MonadValidate monad transformer to collect as many errors as possible and then report all those errors at one go to the user.