fuzz: fix oss-fuzz crash related to channelArgsFromConfig (#11641)

Added regression test to server_corpus

Risk Level: Low
Testing: passes regression test that originally crashed on oss-fuzz
Docs Changes: N/A
Release Notes: N/A

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=22824

Signed-off-by: Arthur Yan <arthuryan@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 019353e8aabd28da8c73204167997cf9e51220a5

envoy/config/core/v3/grpc_service.proto

@@ -209,6 +209,8 @@ message GrpcService {
         // Pointer values are not supported, since they don't make any sense when
         // delivered via the API.
         oneof value_specifier {
+          option (validate.required) = true;
+
           string string_value = 1;
 
           int64 int_value = 2;

envoy/config/core/v4alpha/grpc_service.proto

@@ -215,6 +215,8 @@ message GrpcService {
         // Pointer values are not supported, since they don't make any sense when
         // delivered via the API.
         oneof value_specifier {
+          option (validate.required) = true;
+
           string string_value = 1;
 
           int64 int_value = 2;