Rework camel-jbang-it to support camel-launcher

[jvrubel]

These changes allow customization of the camel command in order to support camel-launcher.

There are also differences from the closed PR with the same title. This one only contains the rework itself alongside some minor fixes. I also greatly simplified it by removing the property out of the container service and keeping it as a simple system property as @mcarlett suggested.

[github-actions]

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[mcarlett]

why you are implementing again what we already have in containerService.executeBackground() ? is this a different behaviour?

[mcarlett]

what do you think to implement a getMainCommand() method in the CliService class so that we have just one place to retrieve the property? you can use so containerService.getMainCommand() instead of MAIN_COMMAND in all the places