Render cri registry mirrors.x.endpoints and configs.x.tls into config_path; keep
using mirrors.x.rewrites and configs.x.auth those do not yet have an
equivalent in the new format.

The new config file format allows disabling containerd's fallback to the
default endpoint when using mirror endpoints; a new CLI flag is added to
control that behavior.

This also re-shares some code that was unnecessarily split into parallel
implementations for linux/windows versions. There is probably more work
to be done on this front but it's a good start.
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>
(cherry picked from commit c45524e6)
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>