feat: add local bzlmod consumer test (googleapis#15339)

This commit adds a minimal Bazel project that consumes google-cloud-cpp
as an external dependency using Bzlmod.

The test is designed to reproduce the canonical repository name mismatch
reported in b/430085995 and will be used to verify that the changes
in this pull request resolve the issue from a downstream user's
perspective.

Author: jinseopkim0

ci/bzlmod_tests/consumer-test/BUILD.bazel

@@ -0,0 +1,9 @@
+load("@rules_cc//cc:defs.bzl", "cc_test")
+
+cc_test(
+    name = "main_test",
+    srcs = ["main.cc"],
+    deps = [
+        "@google_cloud_cpp//google/cloud/storage:storage_client_testing",
+    ],
+)

ci/bzlmod_tests/consumer-test/MODULE.bazel

@@ -0,0 +1,10 @@
+module(name = "bzlmod-consumer-test")
+
+bazel_dep(name = "google_cloud_cpp", version = "3.0.0-rc0")
+bazel_dep(name = "googletest", version = "1.15.2")
+bazel_dep(name = "rules_cc", version = "0.1.1")
+
+local_path_override(
+    module_name = "google_cloud_cpp",
+    path = "/workspace/google-cloud-cpp",
+)

ci/bzlmod_tests/consumer-test/main.cc

@@ -0,0 +1,16 @@
+#include "google/cloud/storage/client.h"
+#include "google/cloud/storage/testing/mock_client.h"
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+TEST(BzlmodTest, CanCreateMockClient) {
+  // Create a mock client.
+  auto mock = std::make_shared<google::cloud::storage::testing::MockClient>();
+
+  // Use the mock to construct a Client object. This verifies that the
+  // necessary symbols are linked correctly.
+  google::cloud::storage::Client client(mock);
+
+  // A simple assertion to make it a valid test.
+  ASSERT_TRUE(true);
+}