add k0s support

[brunnels]

#1120

• Support for k0s
• Replace democratic-csi with openebs-localpath
• Add support for templating into a private Github repo
• Rename bootstrap vars bootstrap_kube_vip_addr -> bootstrap_kubeapi_addr and bootstrap_local_path_provisioner_path -> bootstrap_local_storage_path
• Update Cilium to be 1.15.0 compatible

[onedr0p]

Thanks for taking the time on adding this, great work so far! Few comments on this PR:

1. Completed I think we should have this variable at the top of the config file and renamed from

   # set true to modify templates to work in k0s environment
   k0s:
     enabled: false

   to (hints at talos support someday 😆 )

   # Distribution can either be 'k3s' or 'k0s'
   # Note that changing this to k0s will ignore `system_upgrade_controller` in the addons.
   bootstrap_distribution: k3s

2. Completed I would like to have either openebs-local-storage OR democratic-csi. The latter I've tested or know works on k3s (and talos). I can do testing on my end if you really want to move forward with openebs. It doesn't matter too much to me which solution we choose as long as it has the option to specify the data path on the host in the helm values.

3. Completed system-upgrade-controller will need to be disabled even if the user tries to enable it in the addons when they choose k0s

4. Completed bootstrap_private_github_repo only seems to have checks that verifies the private repo exists, however Flux needs to be modified and a secret needs to be added to support this. I originally left this out because I wanted people to keep it public to get better support. After they had it working and running they could read the README to make it private.

5. k3s needs to have certain metrics dropped in a few places in kube-prometheus-stack, I don't think that should matter too much for k0s. My main question is does k0s work well with monitoring the kubelet, kubeApiServer, kubeControllerManager and kubeEtcd components out of the box or is there something that needs to be enabled or changed in the kube-prometheus-stack Helm values.

6. Completed Lastly, you mentioned the nodes password field in the config. If you want to remove this option and clean up the places it is referenced I am fine with that since SSH done with a private SSH key and the nodes should have passwordless sudo. If not I'll clean it up later.

A couple other areas of improvement would be updating the README and adding support for k0s with renovate if needed.