Move adding ResponseCompression module logic to init_downstream_modules

So that users can override this behavior.

.bleep

@@ -1 +1 @@
-72328c4a1aec58a40b70f82d1144f70c9a19f207
+cab68d4c24c82270ceffef312efc99a3bbc8aaa9

pingora-proxy/src/lib.rs

@@ -766,10 +766,6 @@ where
     SV: ProxyHttp,
 {
     let mut proxy = HttpProxy::new(inner, conf.clone());
-    // Add disabled downstream compression module by default
-    proxy
-        .downstream_modules
-        .add_module(ResponseCompressionBuilder::enable(0));
     proxy.handle_init_modules();
     Service::new(name.to_string(), proxy)
 }

pingora-proxy/src/proxy_trait.rs

@@ -42,8 +42,14 @@ pub trait ProxyHttp {
 
     /// Set up downstream modules.
     ///
-    /// In this phase, users can add or configure modules before the server starts up.
-    fn init_downstream_modules(&self, _modules: &mut HttpModules) {}
+    /// In this phase, users can add or configure [HttpModules] before the server starts up.
+    ///
+    /// In the default implementation of this method, [ResponseCompressionBuilder] is added
+    /// and disabled.
+    fn init_downstream_modules(&self, modules: &mut HttpModules) {
+        // Add disabled downstream compression module by default
+        modules.add_module(ResponseCompressionBuilder::enable(0));
+    }
 
     /// Handle the incoming request.
     ///