Add BUCK file to coreml export script (#5702)

Summary:
Pull Request resolved: #5702

As title, add a target file so we can use it internally
```
 buck run //executorch/examples/apple/coreml/scripts:export  -- -m resnet18
```
ghstack-source-id: 244901220
exported-using-ghexport
bypass-github-export-checks

Reviewed By: shoumikhin

Differential Revision: D63476610

fbshipit-source-id: 908d27ff24335deacbb8a55d1510afac85277f05

examples/apple/coreml/scripts/TARGETS

@@ -0,0 +1,18 @@
+# Any targets that should be shared between fbcode and xplat must be defined in
+# targets.bzl. This file can contain fbcode-only targets.
+load("@fbcode_macros//build_defs:python_binary.bzl", "python_binary")
+
+python_binary(
+    name = "export",
+    srcs = [
+        "export.py",
+    ],
+    main_function = "executorch.examples.apple.coreml.scripts.export.main",
+    deps = [
+        "//executorch/backends/apple/coreml:backend",
+        "//executorch/backends/apple/coreml:partitioner",
+        "//executorch/backends/apple/coreml:quantizer",
+        "//executorch/devtools/etrecord:etrecord",
+        "//executorch/examples/models:models",
+    ],
+)