Introducing Cilium 1.15.1 and Full kube-proxy Replacement

[M4t7e]

This PR introduces Cilium 1.15.1, which supports Kubernetes versions 1.26, 1.27, 1.28, and 1.29.

This will also fix #1210 (#1199). Before this change, Cilium could only run in hybrid kube-proxy replacement mode. Now, full replacement is possible with the newly introduced disable_kube_proxy flag.

Another improvement is the bypassing of iptables connection tracking for Pod traffic in Cilium. This is only effective in native routing mode (cilium_routing_mode = "native").

For the case when eBPF Host-Routing cannot be used and thus network packets still need to traverse the regular network stack in the host namespace, iptables can add a significant cost. This traversal cost can be minimized by disabling the connection tracking requirement for all Pod traffic, thus bypassing the iptables connection tracker.

[mysticaltech]

Simple and neat, yet extra powerful! You are a gem @M4t7e 🙏