* feat: cilium add-mode support
when cni management by kilo is disable, we can use existing cluster's cni setup thanks to add-on mode
https://kilo.squat.ai/docs/introduction#add-on-mode
* feat: manifest example for cilium addon mode
* fix: apply comment from PR review
* fix: add mutex to interface retrieval into flannel addon mode
This commit adds basic support to run in compatibility mode with
Flannel. This allows clusters running Flannel as their principal
networking solution to leverage some advances Kilo features. In certain
Flannel setups, the clusters can even leverage muti-cloud. For this, the
cluster needs to either run in a full mesh, or Flannel needs to use the
API server's external IP address.