CORE-3893 Added isTicketsEnabled check for Data Links UI.

Updated DataActionsMenu to check the value of the new DEProperties::isTicketsEnabled config to determine if the "Manage Data Links" item will be displayed.(cherry picked from commit 2ba20e316c20631daf8fba024c5cfe1a3676c457)
Updated discoveryenvironment-example.properties for v1.6.(cherry picked from commit 8b86487104cc378afc359fd1875e079bcf38ca62)