Added RedisModule_HoldString that either returns a
shallow copy of the given String (by increasing
the String ref count) or a new deep copy of String
in case its not possible to get a shallow copy.
Co-authored-by: Itamar Haber <itamar@redislabs.com>
(cherry picked from commit 4f99b22118ca91e3a7fe9c1c68c19dd717dfdbb5)