[RFC] Change --standalone to bind to a random port (#107734)
Given standalone generates args anyways, it seems like it would be more convenient if it explicitly used a random port by default instead of trying to use 29400.
That way users can directly go with `--standalone` instead of having to spell out `--rdzv-backend=c10d --rdzv-endpoint=localhost:0`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107734
Approved by: https://github.com/H-Huang
