Dynamic platform detection for ImageSpec to support cross-platform development

Signed-off-by: Barry Wu <a0987818905@gmail.com>

Author: BarryWu0812

flytekit/image_spec/image_spec.py

@@ -4,6 +4,7 @@
 import hashlib
 import os
 import pathlib
+import platform
 import re
 import sys
 import typing
@@ -136,6 +137,9 @@ def __post_init__(self):
             # Use the builder with the highest priority by default
             self.builder = max(builder_registry, key=lambda name: builder_registry[name][1])
 
+        if platform.machine() == "arm64":
+            self.platform = "linux/arm64"
+
         parameters_str_list = [
             "packages",
             "conda_channels",