[ENH] - More generic app commands (non-Python)

[mcg1969]

Feature description

Currently the Custom/generic app option is assumed to be run with python -m <ARGS>. This precludes the use of a generic Python script, as opposed to a module, and for that matter a non-Python script.

But the existing Command code is pretty flexible and I would argue it is in no way necessary to be that limiting. We should able to run any script, including non-Python code.

Using simple templating mechanisms already found in the Command class, the port, prefix, etc. for the deployed app can be easily worked into command-line arguments for the command.

Value and/or benefit

The ability to deploy a much wider variety of applications

Anything else?

No response