docs(design-proposal): support CNI Cilium

[Huimintai]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind api-change
/kind bug
/kind cleanup
/kind deprecation
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[huxiaoliang]

comments:

1. how to handle os kernel dependency? since cilium need os kernel >4.9
2. do we need cilium to replace kube-proxy? provide a config parameter?
3. can we support more config parameter?

  cluster-pool-ipv4-cidr: "10.0.0.0/8"
  cluster-pool-ipv4-mask-size: "24"
  disable-cnp-status-updates: "true"

4. tkestack depends on iptable mode 和ipvs mode to support ha and loadbanance, refer to https://github.com/tkestack/tke/blob/master/docs/design-proposals/controlplane-ha-loadbalance.md for the details, please double check this part and highlight in your doc
5. ipv6 support?