Add support for prefix_rewrite and strip_query under RedirectAction (#456)

this patch adds support for dynamically generating redirect msg based on
a request received by modifying the matched prefix or path.

ref: envoyproxy/envoy#2343

Signed-off-by: Madhavan Balasubramanian <bmadhavan@ebay.com>

envoy/api/v2/route/route.proto

@@ -539,8 +539,15 @@ message RedirectAction {
   // The host portion of the URL will be swapped with this value.
   string host_redirect = 1;
 
-  // The path portion of the URL will be swapped with this value.
+  oneof path_rewrite_specifier {
-  string path_redirect = 2;
+    // The path portion of the URL will be swapped with this value.
+    string path_redirect = 2;
+
+    // [#not-implemented-hide:]Indicates that during redirection, the matched prefix (or path)
+    // should be swapped with this value. This option allows redirect URLs be dynamically created
+    // based on the request.
+    string prefix_rewrite = 5;
+  }
 
   enum RedirectResponseCode {
     // Moved Permanently HTTP Status Code - 301.
@@ -565,6 +572,10 @@ message RedirectAction {
 
   // The scheme portion of the URL will be swapped with "https".
   bool https_redirect = 4;
+
+  // [#not-implemented-hide:] Indicates that during redirection, the query portion of the URL will
+  // be removed. Default value is false.
+  bool strip_query = 6;
 }
 
 message DirectResponseAction {