Enable KRUN_INIT_PID1=1 when using krun

### Feature request description

in https://github.com/containers/libkrun/commit/bbaa604784230c3f1b1a37fddec2534480cb3418, libkrun allows bypassing `/init.krun` and using container's own entrypoint as init process. this should be the default behavior for podman (at least when `--init` is not set); it makes behavior coherent with regular `crun` re choice of init, and furthermore allows running systemd in container, and `podman` can be used as a convenient frontend for managing such lightweight microvms with systemd support.

i have a proof-of-concept patch that i tested locally on my nixos configuration. would love to hear if it's a sensible idea and put up the patch if so.

### Suggest potential solution

_No response_

### Have you considered any alternatives?

_No response_

### Additional context

_No response_