Add support for Cilium CNI

[yboaron]

What would you like to be added:

I am creating this issue to track Submariner support for Cilium CNI.

Currently, Cilium CNI is recognized as a generic CNI by Submariner, and subctl verify e2e tests seem to fail on clusters with Cilium CNI.

Why is this needed:

Enable multi-cluster networking using Submariner on clusters with Cilium CNI.

Other Info:

In order to support new CNI in Submariner there is a need to update the following functions:

• CNI network discovery - responsible for pod,service CIDRs and CNI plugin name auto-discovery.
• Submariner RouteAgent handlers (optional) - used to apply configuration specific for CNI, check Calico ippool handler for example.

[dfarrell07]

@gk-fschubert agreed to help with this one in #3159 (comment). Thanks! You can assign yourself here (I'd do it, but can't due to GitHub anti-spam restrictions).