Added benchmark for loading ads descriptor.

Generally this seems to track the speed of loading descriptor.proto.

----------------------------------------------------------------------------------------------------
Benchmark                                                             Time           CPU Iterations
----------------------------------------------------------------------------------------------------
BM_LoadDescriptor_Upb                                             59091 ns      59086 ns      11747   121.182MB/s
BM_LoadAdsDescriptor_Upb                                        4218587 ns    4218582 ns        166   120.544MB/s
BM_LoadDescriptor_Proto2                                         241083 ns     241049 ns       2903   29.7043MB/s
BM_LoadAdsDescriptor_Proto2                                    13442631 ns   13442099 ns         52   34.8975MB/s

benchmarks/BUILD.googleapis

diff --git a/benchmarks/BUILD.googleapis b/benchmarks/BUILD.googleapis
new file mode 100644
index 0000000..c90815b
--- /dev/null
+++ b/benchmarks/BUILD.googleapis
@@ -0,0 +1,29 @@
+load(
+    "@rules_proto//proto:defs.bzl",
+    "proto_library",
+)
+
+proto_library(
+    name = "ads_proto",
+    srcs = glob([
+        "google/ads/googleads/v5/**/*.proto",
+        "google/api/**/*.proto",
+        "google/rpc/**/*.proto",
+        "google/longrunning/**/*.proto",
+        "google/logging/**/*.proto",
+    ]),
+    #srcs = ["google/ads/googleads/v5/services/google_ads_service.proto"],
+    visibility = ["//visibility:public"],
+    deps = [
+       "@com_google_protobuf//:any_proto",
+       "@com_google_protobuf//:empty_proto",
+       "@com_google_protobuf//:descriptor_proto",
+       "@com_google_protobuf//:field_mask_proto",
+       "@com_google_protobuf//:duration_proto",
+       "@com_google_protobuf//:timestamp_proto",
+       "@com_google_protobuf//:struct_proto",
+       "@com_google_protobuf//:api_proto",
+       "@com_google_protobuf//:type_proto",
+       "@com_google_protobuf//:wrappers_proto",
+    ],
+)