feat: Update to OPA v1.2.0 (#373)

Regorus now defaults to rego v1. `import rego.v1` is no longer needed.
Additionally, `future` keywords are automatically imported.

See
https://www.openpolicyagent.org/docs/latest/v0-upgrade/#changes-to-rego-in-opa-v10
to understand the differences between rego v1 and v0.

BREAKING CHANGE:

v0 style policies will error out by default. To enable v0 behavior, call engine.set_rego_v0(true) before
loading policies.

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

bindings/cpp/main.cpp

@@ -6,6 +6,7 @@ void example()
     // Create engine
     regorus::Engine engine;
 
+    engine.set_rego_v0(true);
     engine.set_enable_coverage(true);
     
     // Add policies.
@@ -83,6 +84,7 @@ int main() {
 
     // Create engine.
     regorus::Engine engine;
+    engine.set_rego_v0(true);
 
 
     // Load policies.