[native_assets_cli] Provide an easier way to re(run) builds

Currently the only way to rerun a native assets build build is to invoke: `dart path/to/build.dart --config=.dart_tool/native_assets_builder//config.yaml`. This command is printed when a native build fails if `-v` was passed. Maybe we could provide a better way to run builds.

Possibly: `dart run native_assets_cli:build --package=my_package --os=.. --arch=...` by adding a `bin` script to `package:native_assets_cli`.

@mosuem Did you have any other ideas?