The endpoint attribute worker-threads should be exposed by the template configuration environment variable

For tuning purpose it is necessary to tweak the worker-threads for the endpoint configurtation for HotRod, REST and memcache.
It should be possible to add the attribute to each of the configurations :

<hotrod-connector ... worker-threads=XXXX>
<memcached-connector ... worker-threads=YYYY/>
<rest-connector ... worker-threads=ZZZZ>