feat: or keyword (#315)

Add `or` operator to Rego languages. Available via `rego-extensions`
Cargo feature.

If the evaluated lhs value is not false, null or undefined it is returned.
Otherwise rhs is evaluated and returned.

or operator has least precedence, and is left-associative.

closes #314

Cargo.toml

@@ -67,7 +67,9 @@ full-opa = [
     "time",
     "uuid",
     "urlquery",
-    "yaml"
+    "yaml",
+
+    #"rego-extensions"
 ]
 
 # Features that can be used in no_std environments.
@@ -89,6 +91,9 @@ opa-no-std = [
   "lazy_static/spin_no_std"
 ]
 
+# Rego language extensions
+rego-extensions = []
+
 # This feature enables some testing utils for OPA tests.
 opa-testutil = []
 rand = ["dep:rand"]