docs: Update source branch in kube-proxy-free guide
docs: Update source branch in kube-proxy-free guide

Switch to v1.6, because 1) https://github.com/cilium/cilium/pull/8995
got backported to the v1.6 2) the master templates cannot be used
with the v1.6.0 image due to removed RBAC for "componentstatuses".

Once v1.6.1 is released, we can just include
k8s-install-download-release.rst.

Signed-off-by: Martynas Pumputis <6b0d31c0d563223024da45691584643ac78c96e8@lambda.lt>

cilium/cilium,tgraf/cilium,cilium-team/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,cilium-team/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium