add discord membercount service & endpoint

a background worker is added that sends an approximate member count
request every 60 seconds, caches it into memory, and serves the cache on
a public endpoint

src/router/mod.rs

@@ -1,5 +1,17 @@
-use axum::{Router, routing::get};
+use axum::{Router, http::StatusCode, routing::get};
 
 pub fn init() -> Router {
-    Router::new().route("/", get(async || "root"))
+    Router::new()
+        .route("/", get(async || "root"))
+        .route("/discord/member-count", get(get_member_count))
+}
+
+async fn get_member_count() -> (StatusCode, String) {
+    match crate::discordbot::get_member_count().await {
+        Some(count) => (StatusCode::OK, format!("{count}")),
+        None => (
+            StatusCode::INTERNAL_SERVER_ERROR,
+            format!("An error occured - could not fetch discord member count."),
+        ),
+    }
 }