Different protocols in the same Service definition with type=LoadBalancer (kubernetes#1438)

* First draft for review  of the KEP for Mixed protocol support in Services

* Fix bad spelling and remove template parts based on review comment

* Update OpenStack part with the appropriate Octavia version

* Own findings:
- IBM Cloud CPI and LB functionality got more precise description
- Oracle CPI and LB functionality got more precise description
- Tencent Cloud CPI and LB functionality got more precise description

Review comments:
- Analyze problems with API downgrade/upgrade if this change is implemented
- Change "hardcoded limitation" to "API validation"

* Fix review findings:
- fix the description of the forwarding rule management and billing for different ports with the same protocol
Updates:
- Test plan added
- Graduation criteria added
- Downgrade strategy added
- Version skew strategy added

* Update based on review comments:
- update proposed solution with a better phasing approach throughout the upcoming releases
- update graduation criteria

* Fix review comments:
- add an example, that the CPI could use a new field in Service.status.loadBalancer or a new Event to indicate that the Service object is not acceptable for it for any reasons (e.g. mixed protocols in the Service)
- indicate that the feature flag controls the creation of new Services with mixed protocol config, but not the update operations

* Update ToC and last updated date

* Fix review comments. Add DigitalOcean part

* Fix review comments. Describe in Motivation why billing is a central matter of the KEP

* Fix review comments.

Update AWS information: AWS CPI supports UDP and TCP for AWS NLB.
Be more specific about the selected solution, and the requirements agains the CPIs.
Propose a schema for the extension of the LoadBalancerStatus field in ServiceStatus to provide information about the ports of the load-balancer.x

* Terminate code block for the schema

* Update TOC

* Fix UPD to UDP. Fix last-updated

* GCE internal LB supports different protocols in the forwarding rules.
Move portStatus inside the ingress definition of an LB.
Add a conditions field to the Service.status.loadBalancer and add the first official condition "LoadBalancerMixedProtocolNotSupported to it.

* Move the new conditions from loadbalancer level to the generic Service.Status level

* Add how kube-proxy should use the new port status information

Author: Laszlo Janosi