feat: add command aliasing via PATH lookup

[olamilekan000]

Change adds a feature that allows users to create custom limactl-* commands 
that are automatically discovered and executed when unknown subcommands are used.

implements issue

[jandubois]

I wonder if we should prefix PATH with filepath.Dir(os.Executable()) before launching the plugin, so if the plugin calls limactl it will run the same binary that launched the plugin. Doesn't matter most of the time, but can be helpful when you are testing with e.g. _output/bin/limactl PLUGIN.

[jandubois]

Sorry, noticed one more edge case, but I think after this change it will be good.

[jandubois]

Thanks, LGTM