add authorization example to ro cedar rust hello world

[Swolebrain]

Issue #, if available:
n/a

Description of changes:
just adds an example of using is_authorized to the cedar rust simple examples

[john-h-kastner-aws]

Looks good, though I'm not sure about the CI failures. The oopsla2024 build looks like it's failing for unrelated reasons. Does this build against main? (We should probably add the example for both 4.2 and main branches anyways)

[john-h-kastner-aws]

Nicer API for this:

Suggested change

	let context_json_val = serde_json::json!({});
	let context = Context::from_json_value(context_json_val, None).unwrap();
	let context = Context::empty();

[john-h-kastner-aws]

Suggested change

	let entities_json = r#"[]"#;
	let entities = Entities::from_json_str(entities_json, None).expect("entity parse error");
	let entities = Entities::empty();