ratelimit: allow header descriptors to be skipped (#11153)

Resolves #10124 indirectly by adding an extra config flag to RequestHeaders through which it is possible for descriptors to be sent on a partial match.

Signed-off-by: Rohan Seth <rohan.seth@salesforce.com>

Mirrored from https://github.com/envoyproxy/envoy @ 77e436f9eb39863a4a425bbca9026c86740b36cd

envoy/config/route/v3/route_components.proto

@@ -1395,6 +1395,11 @@ message RateLimit {
 
       // The key to use in the descriptor entry.
       string descriptor_key = 2 [(validate.rules).string = {min_bytes: 1}];
+
+      // If set to true, Envoy skips the descriptor while calling rate limiting service
+      // when header is not present in the request. By default it skips calling the
+      // rate limiting service if this header is not present in the request.
+      bool skip_if_absent = 3;
     }
 
     // The following descriptor entry is appended to the descriptor and is populated using the

envoy/config/route/v4alpha/route_components.proto

@@ -1376,6 +1376,11 @@ message RateLimit {
 
       // The key to use in the descriptor entry.
       string descriptor_key = 2 [(validate.rules).string = {min_bytes: 1}];
+
+      // If set to true, Envoy skips the descriptor while calling rate limiting service
+      // when header is not present in the request. By default it skips calling the
+      // rate limiting service if this header is not present in the request.
+      bool skip_if_absent = 3;
     }
 
     // The following descriptor entry is appended to the descriptor and is populated using the