feat: Add stopsignal to container lifecycle field in podspec

[saolof]

Addresses #25389

* Supported a StopSignal LifeCycle field in podman kube files, following KEP-4960 implemented in kubernetes 1.33.

Since the CLI and quadlets support the docker --stopsignal flag, it does look like the code does only needs a change to one place in the specgen to handle it in kube files as well. I may be wrong about this, let me know if I am

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[giuseppe]

can we use SignalMap we already have in pkg/signal?

[saolof]

I just copied the type definitions from the upstream kubernetes API. As for using the SignalMap, I'm not sure if openapi spec generation will work if the constant values aren't defined in the same file as the +enum definition. If that isn't being used I could just leave this as type Signal string and nothing else for the sake of yaml parsing and then the ParseSignal function will validate it using the map either way.