Entry point should be optional when running sonobuoy gen plugin

[stmcginnis]

Describe the solution you'd like
[A clear and concise description of what you want to happen.]

Currently when running sonobuoy gen plugin you need to either specify -c $ENTRYPOINT or use the default entrypoint of ./run.sh. For some test plugins though, it may be easier to just go with the container image's already defined entrypoint. If the container image was made specifically for running these tests, then it just needs to be run and the entrypoint does not need to be explicitly provided.

For running a set of plugins where there may be a mix of entrypoints, it's certainly possible to inspect the container image to see its entrypoint, then pass that in to the sonobuoy gen plugin call so they match. But especially when things are being scripted, this adds some extra complexity. Another option given was to just remove the entrypoint line from the resulting YAML emitted from sonobuoy gen plugin, which is probably an easier option.

It would be nice to either not have this requirement, or to have a way to pass something like -c "" to the command to have it skip including the entrypoint in the plugin YAML.

Some discussion here: https://kubernetes.slack.com/archives/C6L3G051C/p1661179994256429

[stale]

There has not been much activity here. We'll be closing this issue if there are no follow-ups within 15 days.

[stmcginnis]

Hoping to keep this around. I may be able to spend some time on it soon.