Update virtualservice HTTPRetry docs for the attempt field (#2919)

* Update virtualservice HTTPRetry docs for the `attempt` field

* update  files with docs

Author: Smeb

networking/v1alpha3/virtual_service.pb.go

@@ -1793,7 +1793,8 @@ message HTTPRetry {
   // between retries will be determined automatically (25ms+). When request
   // `timeout` of the [HTTP route](https://istio.io/docs/reference/config/networking/virtual-service/#HTTPRoute)
   // or `per_try_timeout` is configured, the actual number of retries attempted also depends on
-  // the specified request `timeout` and `per_try_timeout` values.
+  // the specified request `timeout` and `per_try_timeout` values. MUST BE >= 0. If `0`, retries will be disabled.
+  // The maximum possible number of requests made will be 1 + `attempts`.
   int32 attempts = 1 [(google.api.field_behavior) = REQUIRED];
 
   // Timeout per attempt for a given request, including the initial call and any retries. Format: 1h/1m/1s/1ms. MUST BE >=1ms.

networking/v1alpha3/virtual_service.pb.html

@@ -1793,7 +1793,8 @@ message HTTPRetry {
   // between retries will be determined automatically (25ms+). When request
   // `timeout` of the [HTTP route](https://istio.io/docs/reference/config/networking/virtual-service/#HTTPRoute)
   // or `per_try_timeout` is configured, the actual number of retries attempted also depends on
-  // the specified request `timeout` and `per_try_timeout` values.
+  // the specified request `timeout` and `per_try_timeout` values. MUST BE >= 0. If `0`, retries will be disabled.
+  // The maximum possible number of requests made will be 1 + `attempts`.
   int32 attempts = 1 [(google.api.field_behavior) = REQUIRED];
 
   // Timeout per attempt for a given request, including the initial call and any retries. Format: 1h/1m/1s/1ms. MUST BE >=1ms.