[Release 1.21] RKE2 Can't Run Workloads with Default Msft Pause Image

[luthermonson]

Booting rke2 without setting the pause image results in using the build tag compiled version which pointed to mcr.microsoft.com. The code to pull default images forces docker.io as a repo and tries to force pulling non-existing images if you do not override the pause image.

[rancher-max]

Validated on v1.21.3-rc3+rke2r2 the pause image is working correctly now.