message: Add `AWS_REGION` env for S3 in TensorFlow
  This fix tries to address the issue raised in 14951 where
  the region can only be specified with non-common `S3_REGION`
  environment variables.
  This fix adds the support of `AWS_REGION` which takes precedence
  over `S3_REGION`.
  This fix fixes 14951.
diff: @@ -12,9 +12,9 @@ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  ==============================================================================*/
  +#include "tensorflow/core/platform/s3/s3_file_system.h"
  #include "tensorflow/core/lib/io/path.h"
  #include "tensorflow/core/platform/mutex.h"
  -#include "tensorflow/core/platform/s3/s3_file_system.h"
  #include "tensorflow/core/platform/s3/s3_crypto.h"
  #include <aws/core/Aws.h>
  @@ -49,10 +49,16 @@ Aws::Client::ClientConfiguration& GetDefaultClientConfig() {
  if (endpoint) {
  cfg.endpointOverride = Aws::String(endpoint);
  }
  + const char* region = getenv("AWS_REGION");
  + if (region) {
  + cfg.region = Aws::String(region);
  + } else {
  + // TODO (yongtang): `S3_REGION` should be deprecated after 2.0.
  const char* region = getenv("S3_REGION");
  if (region) {
  cfg.region = Aws::String(region);
  }
  + }
  const char* use_https = getenv("S3_USE_HTTPS");
  if (use_https) {
  if (use_https[0] == '0') {
  