We are currently loading plugin command stubs for every
invocation which still has a significant performance hit.
With this change we are doing this operation only if cobra
completion arg request is found.
- 20.10.23: `docker --version` takes ~15ms
- 23.0.1: `docker --version` takes ~93ms
With this change `docker --version` takes ~9ms
Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>