feat: increase HSTS age to one month

New HSTS preload guidelines suggest to me that any further changes
(including enabling preloading) are unnecessary these days as browsers
will automatically try to upgrade to HTTPS anyway.

server/src/main.rs

···
                 .layer(CompressionLayer::new())
                 .layer(SetResponseHeaderLayer::overriding(
                     HeaderName::from_static("strict-transport-security"),
-                    HeaderValue::from_static("max-age=300; includeSubDomains"),
+                    HeaderValue::from_static("max-age=2592000; includeSubDomains"),
                 )),
         );