Add ratelimiting example

Was really supposed to add this earlier but I forgot about it.  Oops

examples/ratelimits.rs

@@ -0,0 +1,39 @@
+use anyhow::*;
+use futures_core::future::BoxFuture;
+use futures_util::FutureExt;
+use log::LevelFilter;
+use northstar::{Server, Request, Response, GEMINI_PORT, Document};
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    env_logger::builder()
+        .filter_module("northstar", LevelFilter::Debug)
+        .init();
+
+    let two = std::num::NonZeroU32::new(2).unwrap();
+
+    Server::bind(("localhost", GEMINI_PORT))
+        .add_route("/", handle_request)
+        .rate_limit("/limit", northstar::Quota::per_minute(two))
+        .serve()
+        .await
+}
+
+fn handle_request(request: Request) -> BoxFuture<'static, Result<Response>> {
+    async move {
+        let mut document = Document::new();
+
+        if let Some("limit") = request.trailing_segments().get(0).map(String::as_str) {
+            document.add_text("You're on a rate limited page!")
+                    .add_text("You can only access this page twice per minute");
+        } else {
+            document.add_text("You're on a normal page!")
+                    .add_text("You can access this page as much as you like.");
+        }
+        document.add_blank_line()
+                .add_link("/limit", "Go to rate limited page")
+                .add_link("/", "Go to a page that's not rate limited");
+        Ok(Response::document(document))
+    }
+    .boxed()
+}