feat: introduce reset flag and routine

[deviantony]

This PR adds a -reset flag that can be used when starting k2d. When this flag is enabled, k2d will clean up all the resources created by k2d and via k2d (this include any workload and data created through k2d).

It can be used via:

docker run -it \
  --name k2d \
  --volume /var/run/docker.sock:/var/run/docker.sock \
  --volume /var/lib/k2d:/var/lib/k2d \
  portainer/k2d:1.0.0-beta -reset

Closes #64