Serverless support

[kerthcet]

What would you like to be added:

Some of the options:

• https://github.com/knative/serving
• https://github.com/openfaas/faas

Why is this needed:

Completion requirements:

This enhancement requires the following artifacts:

• [x] Design doc
• [x] API change
• [x] Docs update

The artifacts should be linked in subsequent comments.