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: d94c733ee2bfaedd9a1c45d58fbd56c99403c94d
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
