feat(pd): specific error msg for auto https

Adding a specific error message for a failure mode of `pd` when using
`--grpc-auto-https`: if run as a normal user, the bind to 443 will fail.
That's OK, but state clearly what operation failed. Without this change,
the error message is simply "Permission denied", with no mention of the
attempted bind on 443.

crates/bin/pd/src/main.rs

@@ -428,7 +428,10 @@ async fn main() -> anyhow::Result<()> {
                         .parse()
                         .context("failed to parse grpc_bind address")?,
                 );
-                let listener = TcpListenerStream::new(TcpListener::bind(grpc_bind).await?);
+                let bound_listener = TcpListener::bind(grpc_bind)
+                    .await
+                    .context(format!("Failed to bind HTTPS listener on {}", grpc_bind))?;
+                let listener = TcpListenerStream::new(bound_listener);
                 // Configure HTTP2 support for the TLS negotiation; we also permit HTTP1.1
                 // for backwards-compatibility, specifically for grpc-web.
                 let alpn_config = vec!["h2".into(), "http/1.1".into()];