Replace k3s/rke2 kdm requests with new endpoints

[richard-cox]

RFD: https://github.com/SUSE/rancher-architecture/pull/26

Blocked on rancher/rancher#50017

• Remove fall backs on /v1-k3s-release/channels + /v1-rke2-release/channels to determine default k3s/rke2 version (contain bad info)
• Replace
  • GET /v1-{K3s|rke2}-release/releases with POST to /v1/ext.cattle.io.kdmrequests
  • POST v3/kontainerdrivers?action=refresh with POST to /v1/ext.cattle.io.kdmrefreshrequests
    • permissions should be checked given schema containing POST for this type

[nwmac]

@richard-cox I'm assuming we'll bump this to 2.16?