Add retriable headers retry policy. (#8187)

Configured via 'retriable-headers' retry policy and 'retriable_headers'
list of headers (both can be set via config or request headers) . If the
upstream response has any of the retriable headers set, retry will be
triggered.

Signed-off-by: Oleg Shaldibin <olegsh@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 81460d8482b73ba70ea15b76163a7c645e2a7b96

envoy/api/v2/route/route.proto

@@ -848,7 +848,7 @@ message RouteAction {
 }
 
 // HTTP retry :ref:`architecture overview <arch_overview_http_routing_retry>`.
-// [#comment:next free field: 9]
+// [#comment:next free field: 10]
 message RetryPolicy {
   // Specifies the conditions under which retry takes place. These are the same
   // conditions documented for :ref:`config_http_filters_router_x-envoy-retry-on` and
@@ -933,6 +933,11 @@ message RetryPolicy {
   // the base interval. The documentation for :ref:`config_http_filters_router_x-envoy-max-retries`
   // describes Envoy's back-off algorithm.
   RetryBackOff retry_back_off = 8;
+
+  // HTTP headers that trigger a retry if present in the response. A retry will be
+  // triggered if any of the header matches match the upstream response headers.
+  // The field is only consulted if 'retriable-headers' retry policy is active.
+  repeated HeaderMatcher retriable_headers = 9;
 }
 
 // HTTP request hedging :ref:`architecture overview <arch_overview_http_routing_hedging>`.