fix(connlib): make Relay connectivity error log at ERROR level (#6105)

This almost always indicate a user-impacting connectivity error. For
customers troubleshooting their Gateways by greping for `ERROR`, this
will make these much easier to find.

---------

Signed-off-by: Jamil <jamilbk@users.noreply.github.com>

rust/connlib/snownet/src/node.rs

@@ -449,7 +449,7 @@ where
         self.allocations
             .retain(|rid, allocation| match allocation.can_be_freed() {
                 Some(e) => {
-                    tracing::info!(%rid, "Disconnecting from relay; {e}");
+                    tracing::error!(%rid, "Disconnecting from relay; {e}");
 
                     false
                 }