Add swagger definitions for APIs

[adleong]

It would be great to have some kind of formal specification for the APIs in this repo; swagger, for example.

[stefanprodan]

A formal specification for the APIs (except for metrics) is here: https://github.com/servicemeshinterface/smi-sdk-go/tree/master/crds I've added OpenAPI schema to all CRDs.

[stefanprodan]

We could move the CRDs in this repo or move the metrics OpenAPI definition in the SDK, it's going to be very confusing if we don't use a single repo for all definitions.

[tomkerkhove]

I think that sounds fair to have the definition in this repo.