Endpoint Name should also follow DNS1123 rule to have Maxlength=63 chars

[yangcao77]

The schema limits endpoint name with Maxlength=15 is because the pod container port name has that limitation

Since we want to use <portNumber>-<protocol> as pod container port name (#287), the Endpoint Name won't have that 15 chars limitation; it should follow DNS1123 rule, to be with maxlength=63