fuzz: add bounds to statsh flush interval (envoyproxy#8043)

Add PGV bounds to the stats flush interval (greater than 1ms and less than 5000ms) to prevent Envoy from hanging from too small of a flush time.

Risk Level: Low
Testing: Corpus Entry added
Fixes OSS-Fuzz issue
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=16300

Signed-off-by: Asra Ali <asraa@google.com>

api/envoy/config/bootstrap/v2/bootstrap.proto

@@ -99,7 +99,14 @@ message Bootstrap {
   // performance reasons Envoy latches counters and only flushes counters and
   // gauges at a periodic interval. If not specified the default is 5000ms (5
   // seconds).
-  google.protobuf.Duration stats_flush_interval = 7 [(gogoproto.stdduration) = true];
+  // Duration must be at least 1ms and at most 5 min.
+  google.protobuf.Duration stats_flush_interval = 7 [
+    (validate.rules).duration = {
+      lt: {seconds: 300},
+      gte: {nanos: 1000000}
+    },
+    (gogoproto.stdduration) = true
+  ];
 
   // Optional watchdog configuration.
   Watchdog watchdog = 8;

test/server/server_corpus/clusterfuzz-testcase-server_fuzz_test-5734693923717120

@@ -0,0 +1,18 @@
+static_resources {
+  clusters {
+    name: "@"
+    connect_timeout {
+      nanos: 250000000
+    }
+    common_lb_config {
+      zone_aware_lb_config {
+        min_cluster_size {
+          value: 38
+        }
+      }
+    }
+  }
+}
+stats_flush_interval {
+  nanos: 32256
+}

test/server/server_fuzz_test.cc

@@ -1,5 +1,7 @@
 #include <fstream>
 
+#include "envoy/config/bootstrap/v2/bootstrap.pb.validate.h"
+
 #include "common/network/address_impl.h"
 #include "common/thread_local/thread_local_impl.h"