for-each-ref: add '--contains' option

for-each-ref: add '--contains' option

Add the '--contains' option provided by 'ref-filter'. The '--contains'
option lists only refs which contain the mentioned commit (HEAD if no
commit is explicitly given).

Add documentation and tests for the same.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>