Refine the "not support" error when searching user (#14696)
Refine the "not support" error when searching user (#14696)

If authenticator does not support searching user/group, wraps it as a
not found error, such that the API will return 404 rather than confusing
500.

Signed-off-by: Daniel Jiang <b8e1ca884a84f218767196db52915b5edb9f310e@vmware.com>
wy65701436/harbor,reasonerjt/harbor,wy65701436/harbor,wy65701436/harbor,reasonerjt/harbor,reasonerjt/harbor,reasonerjt/harbor,reasonerjt/harbor,wy65701436/harbor,reasonerjt/harbor,wy65701436/harbor,wy65701436/harbor