add serde default attribute for ResolverOpts

.gitignore

@@ -1,4 +1,5 @@
 .vscode/
+.idea/
 
 *.swp
 

crates/resolver/src/config.rs

@@ -499,6 +499,7 @@ impl Default for LookupIpStrategy {
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
 #[cfg_attr(feature = "serde-config", derive(Serialize, Deserialize))]
 #[allow(dead_code)] // TODO: remove after all params are supported
+#[serde(default)]
 pub struct ResolverOpts {
     /// Sets the number of dots that must appear (unless it's a final dot representing the root)
     ///  that must appear before a query is assumed to include the TLD. The default is one, which