Max heap fix (#7016)

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

Mirrored from https://github.com/envoyproxy/envoy @ e4d2bf442ba32c6df7ff1cb879304b22255eb674

envoy/config/resource_monitor/fixed_heap/v2alpha/fixed_heap.proto

@@ -7,11 +7,13 @@ option java_multiple_files = true;
 option java_package = "io.envoyproxy.envoy.config.resource_monitor.fixed_heap.v2alpha";
 option go_package = "v2alpha";
 
+import "validate/validate.proto";
+
 // [#protodoc-title: Fixed heap]
 
 // The fixed heap resource monitor reports the Envoy process memory pressure, computed as a
 // fraction of currently reserved heap memory divided by a statically configured maximum
 // specified in the FixedHeapConfig.
 message FixedHeapConfig {
-  uint64 max_heap_size_bytes = 1;
+  uint64 max_heap_size_bytes = 1 [(validate.rules).uint64.gt = 0];
 }