Enable v1beta3 API via --runtime_config=api/v1beta3 flag

This exposes the proper v1beta3 API endpoint when the user specifies
the --runtime_config=api/v1beta3 argument to the apiserver. v1beta3
is still considered experimental and subject to change.

--runtime_config is a map of string keys and values, that can be
specified by providing

    --runtime_config=a=b,b=c,d,e

Only the key must be specified, the value can be omitted.

Enables v1beta3 in hack/local-up-cluster.sh and hack/test-cmd.sh
Add Type() method on flags for compat with pflag library

Allows our flag objects to be used with both golang flags and pflags