[native_assets_cli] HookConfig should have a targetIosVersion

[dcharkes]

Context:

• [native_assets] There's two errors thrown by Xcode 15.3 when submitting Flutter apps built with native_assets to the App Store. flutter/flutter#148044

This would enable build and link hooks to fail if they cannot produce native code assets with that iOS SDK version.

Standalone Dart packages do not specify a minimum iOS version unlike Flutter plugins. Instead the flow with standalone packages with native assets is to get the ios target version as config value from the Flutter tools invocation.

[dcharkes]

Maybe xcodebuild can also consume a desired ios target version. Then we also want to plumb it through in package:native_toolchain_c.