[RFC/v3] Presets in Permissions

rfcs/Presets in Permissions.md

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+# Presets in Permissions
+
+As a part of command permissions, we want to be able to control what values for an argument a particular role can pass.
+
+The following changes are proposed to the metadata.
+
+For command permissions, allow specifying a set of argument values which will be preset. Arguments which have been preset no longer get generated in the GraphQL schema.
+
+```yaml
+kind: CommandPermissions
+version: v1
+definition:
+  commandName: delete_user
+  permissions:
+    - role: user
+      allowExecution: true
+      argumentPresets:
+        - argument: user_id
+          value:
+            sessionVariable: x-hasura-user-id
+```
+
+A similar change would be required for model arguments / ModelPermissions.
+
+Also, for supporting complex input objects, we will allow input presets in TypePermissions as well
+
+```yaml
+kind: TypePermissions
+version: v1
+definition:
+  typeName: DeleteUserInput
+  permissions:
+    - role: user
+      input:
+        fieldPresets:
+          - field: is_frozen
+            value:
+              literal: false
+```
+Any field which has been preset will not be generated in the GraphQL schema. If all fields of a type have been preset then the parent field / argument will not be generated.