Adding Greek Language mailing list in the corresponding puppet module

Following the same structure as other language specific lists,
an addition for the 'openstack-el' mailing list is proposed.
Please note that 'EL' is the corresponding 2 letter ISO for Greek.

Change-Id: Ie430595e078c5ecfe215fd176b9bbf96cc4b4bba
Merge "Adding Greek Language mailing list in the corresponding puppet module"