Feature request: string interpolate in magic arguments

I'd like to use "${XXX}" or "$XXX" style string interpolate in magic arguments. So I can run dynamic magic programmatically, for example:

```
String classifier = System.getProperty("os.name").startsWith("Mac") ? "osx-x86_64" : "linux-x86_64";

%maven ai.djl.mxnet:mxnet-native-mkl:jar:${classifier}:1.6.0-a-SNAPSHOT
```

 