Cross-compiling from Ubuntu for aarch64

In the table of supported platforms it looks like the only way to target arm64 architecture for lambda is to compile on Amazon Linux 2.

Would it be possible to support cross-compiling from other OS's? Specifically Ubuntu 22.04?

My lambda function seems to build fine but its an error in the packaging stage:

```
cd .../build/lambda/src/aws && ../../vcpkg_installed/arm64-linux-release/share/aws-lambda-runtime/packager .../build/lambda/src/aws/test_lambda
not a dynamic executable
make[3]: *** [src/aws/CMakeFiles/aws-lambda-package-test_lambda.dir/build.make:73: src/aws/CMakeFiles/aws-lambda-package-test_lambda] Error 1
make[3]: Leaving directory '.../build/lambda'
make[2]: *** [CMakeFiles/Makefile2:3032: src/aws/CMakeFiles/aws-lambda-package-test_lambda.dir/all] Error 2
make[2]: Leaving directory '.../build/lambda'
make[1]: *** [CMakeFiles/Makefile2:3039: src/aws/CMakeFiles/aws-lambda-package-test_lambda.dir/rule] Error 2
make[1]: Leaving directory '..../build/lambda'
make: *** [Makefile:213: src/aws/CMakeFiles/aws-lambda-package-test_lambda.dir/rule] Error 2
```