find_package: Make config-mode success message match FPHSA
When a find module using FindPackageHandleStandardArgs succeeds, it prints a one-line "Found ..." status message if
find_package was called without the
QUIET option. We should consider doing this automatically in
CONFIG mode too when the package configuration file is found. This will require a policy for compatibility.
For reference, !851 (merged) already made the config-mode not-found message match FPHSA.