Merge pull request kubernetes#48861 from mbohlool/openapi_aggr

Automatic merge from submit-queue (batch tested with PRs 49992, 48861, 49267, 49356, 49886)

Reintegrate aggregation support for OpenAPI

Reintegrating changes of kubernetes#46734

Changes summary:

- Extracted all OpenAPI specs to new repo `kube-openapi`
- Make OpenAPI spec aggregator to copy and rename any non-requal model (even with documentation change only).
- Load specs when adding APIServices and retry on failure until successful spec retrieval or a 404.
- Assumes all Specs except aggregator's Spec are static 
- A re-register of any APIService will result in updating the spec for that service (Suggestion for TPR: they should be registered to aggregator API Server, Open for discussion if any more changes needed for another PR.)

fixes kubernetes#48548