Automatic merge from submit-queue (batch tested with PRs 49665, 49689, 49495, 49146, 48934)

make it possible to allow discovery errors for controllers

Update the discovery client to return partial discovery information *and* an error.  Since we can aggregate API servers, discovery of some resources can fail independently.  Callers of this function who want to tolerate the errors can, existing callers will still get an error and fail in normal blocks.

@kubernetes/sig-api-machinery-misc @sttts