refactor: derive Clone for IOx client builder

Allows an IOx client builder (with its associated configuration) to be
cloned.

client_util/src/connection.rs

@@ -68,7 +68,7 @@ pub type Result<T, E = Error> = std::result::Result<T, E>;
 ///     .expect("connection must succeed");
 /// # }
 /// ```
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct Builder {
     user_agent: String,
     headers: Vec<(HeaderName, HeaderValue)>,
@@ -171,3 +171,15 @@ impl Builder {
         Self { timeout, ..self }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_builder_cloneable() {
+        // Clone is used by Conductor.
+        fn assert_clone<T: Clone>(_t: T) {}
+        assert_clone(Builder::default())
+    }
+}