HandlePluginCommand receives a pluginHandler and command-line arguments and attempts to find a plugin executable on the PATH that satisfies the given arguments.

NewDefaultKubectlCommand creates the `kubectl` command with default arguments.

NewDefaultKubectlCommandWithArgs creates the `kubectl` command with arguments.

NewDefaultPluginHandler instantiates the DefaultPluginHandler with a list of given filename prefixes used to identify valid plugin filenames.

NewKubectlCommand creates the `kubectl` command and its nested children.

DefaultPluginHandler implements PluginHandler.

PluginHandler is capable of parsing command line arguments and performing executable filename lookups to search for valid plugin files, and execute found plugins.