specify listener in error messages and logs

The "listening for incoming traffic on ..." log line is new, but
something I've wanted even when we only supported one listener.

I considered getting rid of `clippy::too_many_lines` by factoring out
the construction of `app` to a separate function, but found that
specifying it's type (or relevant traits) got quite hairy.

src/config.rs

@@ -1,5 +1,6 @@
 use std::{
     borrow::Cow,
+    fmt::{self, Display},
     net::{IpAddr, Ipv4Addr},
     path::{Path, PathBuf},
 };
@@ -96,7 +97,7 @@ pub(crate) struct TlsConfig {
     pub(crate) key: String,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 #[serde(tag = "type", rename_all = "snake_case")]
 pub(crate) enum ListenConfig {
     Tcp {
@@ -109,6 +110,23 @@ pub(crate) enum ListenConfig {
     },
 }
 
+impl Display for ListenConfig {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ListenConfig::Tcp {
+                address,
+                port,
+                tls: false,
+            } => write!(f, "http://{address}:{port}"),
+            ListenConfig::Tcp {
+                address,
+                port,
+                tls: true,
+            } => write!(f, "https://{address}:{port}"),
+        }
+    }
+}
+
 fn false_fn() -> bool {
     false
 }