Currently, openapiv3 discovery uses requestURI to discover resources.
However, that does not work when the rest endpoint contains prefixes
(e.g. `http://localhost/test-endpoint/`).
Because requestURI overwrites prefixes also in rest endpoint
(e.g. `http://localhost/openapiv3/apis/apps/v1`).
Since `absPath` keeps the prefixes in the rest endpoint,
this PR changes to absPath instead requestURI.
Kubernetes-commit: ee1d7eb5d82f3b2a76afc57bc33bc7e08c34bf27
reflect latest struct changes
use correct discovery openapi test data layout
make the OpenAPIv3 interface less blue
field grouping
add copyrights
implement cached discovery client
add cached discovery tests
address review feedback
Kubernetes-commit: 075866b3e3ea029c243d82d8d6eb99e96d9c49d3
