Build with System OpenSSL on Mac OS arm64 (#31096)

* fix: grpcio fails to build from source on Apple Silicon mac #(25082)

Boringssl currently does not support macOS arm64, so installation on these platform with default config will undoubtedly fail, that means the env var 'BUILD_WITH_SYSTEM_OPENSSL' must be set to true.

* Use system installation of openssl by default on macOS arm64

* Format code by yapf

setup.py

@@ -133,11 +133,22 @@ BUILD_OVERRIDE_BORING_SSL_ASM_PLATFORM = os.environ.get(
 # present, then it will still attempt to use Cython.
 BUILD_WITH_CYTHON = _env_bool_value('GRPC_PYTHON_BUILD_WITH_CYTHON', 'False')
 
+# Currently, boringssl does not support macOS arm64, so we try to use the system
+# installation of openssl to build gRPC locally by default.
+if "darwin" in sys.platform and "arm64" == platform.machine().lower():
+    sys.stderr.write(
+        "Boringssl currently does not support macOS arm64, so we'll try to use the system installation "
+        "of 'openssl' to build by default, make sure you have 'openssl' installed in this case\n"
+    )
+    BUILD_WITH_SYSTEM_OPENSSL_DEFAULT_ENV = "True"
+else:
+    BUILD_WITH_SYSTEM_OPENSSL_DEFAULT_ENV = "False"
+
 # Export this variable to use the system installation of openssl. You need to
 # have the header files installed (in /usr/include/openssl) and during
 # runtime, the shared library must be installed
-BUILD_WITH_SYSTEM_OPENSSL = _env_bool_value('GRPC_PYTHON_BUILD_SYSTEM_OPENSSL',
-                                            'False')
+BUILD_WITH_SYSTEM_OPENSSL = _env_bool_value(
+    'GRPC_PYTHON_BUILD_SYSTEM_OPENSSL', BUILD_WITH_SYSTEM_OPENSSL_DEFAULT_ENV)
 
 # Export this variable to use the system installation of zlib. You need to
 # have the header files installed (in /usr/include/) and during