[FEATURE] Update hardcoded k3s version

[musjj]

Is your feature request related to a problem or a Pull Request

The hardcoded k3s version is pinned to a very old version:

k3d/version/version.go

Line 41 in 0a18d07

var K3sVersion = "v1.21.7-k3s1"

This caused quite a few puzzling issues for me, such as missing feature flags:

E0225 16:36:19.223608      87 server.go:185] "Failed to set feature gates from initial flags-based config" err="unrecognized feature gate: KubeletInUserNamespace"

Scope of your request

An update to the k3s version.

Describe the solution you'd like

The default k3s version should be kept updated. Maybe there should be a CI that automatically bumps it on new versions.

Describe alternatives you've considered

Manually specify the version (e.g. --image=rancher/k3s:v1.32.1-k3s1).