Add support for OS- and CPU- specific artifacts when downloading from NATS

[autodidaddict]

Proposed change

Add a bit of intelligence to artifact downloading:

• If the workload type is function (JavaScript or wasm), no changes
• If the workload type is native:
  • Attempt to download {path}_{os}_{arch} (e.g. echoservice_darwin_amd64) where os and arch are the operating system and CPU architecture of the Nex node attempting to download the artifact
  • If no such artifact exists, try and download just {path}

Use case

In the current version of Nex, it will pull whatever artifact is indicated by the URL in the start workload request. This means that if you accidentally give Nex the URL for a darwin artifact and send it to a Nex node running on Linux, the workload will fail to start.

This would allow for Nex nodes running on different CPUs and operating systems to all be given the same start workload command and it will "just work" and download the appropriate binary

Contribution

No response