[PATCH v2] app/test-pmd: add generic PROG action parser support

[Ajmera, Megha]

> 
> Ran AI review on this manually since that gets better context.
> The feedback was:
> 
Thanks for the review. I have addressed most of the comments in v3 patch.

Comment #11 is intentionally not applied. In the PROG argument parser path, push_args() stores pointers to struct arg entries in ctx->args, and those entries are consumed later by subsequent parser callbacks (parse_int() / parse_string()), not within the same helper call. So if the helper used stack-local struct arg, those pointers would become invalid after return (use-after-scope).