Refactor input parsing in v0 API
Refactor input parsing in v0 API

Previously the server was using the Rego parse to conveniently parse
inputs into ast.Value. For large inputs this was taking unnecessarily
long (e.g., 60s for 500KB of JSON.)

tsandall/opa,open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,open-policy-agent/opa,tsandall/opa,tsandall/opa,tsandall/opa