feat: Add environment credentials feature tracking to User-Agent

- Add CREDENTIALS_ENV_VARS enum to UserAgentFeature with metric ID 'g'
- Track environment credentials usage in AWSClient::AttemptOneRequest
- Check for AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY presence
- Implements env-credentials SEP specification for business metrics
- Add unit test for environment credentials feature tracking

Resolves environment credentials tracking for User-Agent 2.1 business metrics.

Author: kai-ion

tests/aws-cpp-sdk-monitoring-unit-tests/CloudWatchUnitTest.cpp

@@ -75,8 +75,8 @@ class ClientHolder {
   CloudWatchClient client;
 };
 
-#ifdef ENABLED_ZLIB_REQUEST_COMPRESSION
 TEST_F(CloudWatchTest, TestUserAgentCompressionTracking) {
+#if defined(ENABLED_ZLIB_REQUEST_COMPRESSION) && ENABLED_ZLIB_REQUEST_COMPRESSION == 1
   // Setup mock response with proper CloudWatch XML
   std::shared_ptr<HttpRequest> requestTmp =
       CreateHttpRequest(Aws::Http::URI("dummy"), Aws::Http::HttpMethod::HTTP_POST, Aws::Utils::Stream::DefaultResponseStreamFactoryMethod);
@@ -115,7 +115,6 @@ TEST_F(CloudWatchTest, TestUserAgentCompressionTracking) {
 
   request.AddMetricData(metricDatum);
 
-  std::cout << "=== Making CloudWatch request with 20KB payload ===" << std::endl;
   auto outcome = client.PutMetricData(request);
   AWS_ASSERT_SUCCESS(outcome);
 
@@ -125,25 +124,14 @@ TEST_F(CloudWatchTest, TestUserAgentCompressionTracking) {
   const auto& userAgent = lastRequest.GetUserAgent();
   EXPECT_TRUE(!userAgent.empty());
 
-  std::cout << "User-Agent: " << userAgent << std::endl;
-
   const auto userAgentParsed = Aws::Utils::StringUtils::Split(userAgent, ' ');
-  std::cout << "User-Agent parts: ";
-  for (const auto& part : userAgentParsed) {
-    std::cout << "[" << part << "] ";
-  }
-  std::cout << std::endl;
 
   // Check for gzip compression business metric (L) in user agent
   auto businessMetrics = std::find_if(userAgentParsed.begin(), userAgentParsed.end(),
       [](const Aws::String& value) { return value.find("m/") != Aws::String::npos && value.find("L") != Aws::String::npos; });
 
-  if (businessMetrics != userAgentParsed.end()) {
-    std::cout << "Found compression metric: " << *businessMetrics << std::endl;
-  } else {
-    std::cout << "Compression metric 'L' not found in User-Agent" << std::endl;
-  }
-  
   EXPECT_TRUE(businessMetrics != userAgentParsed.end());
-}
-#endif // ENABLED_ZLIB_REQUEST_COMPRESSION
+#else
+  GTEST_SKIP() << "ZLIB compression not available in this build";
+#endif
+}