examples: Fix docker-compose mount points
examples: Fix docker-compose mount points

- Add /var/run/netns which is needed for named netns of
  cilium-health ep.
- Document netns related mounts.
- Remove unnecessary /run/docker/plugins mount from cilium-agent
  container, as cilium-agent does not need to access any plugin
  socket.

NOTE: we use `rshared` mount propagation for netns related mounts
to prevent from possibly leaking netns. See for more details:
https://github.com/moby/moby/issues/32090.

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

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