Add YuniKorn internal domain name to yunikorn-scheduler-interface

We already have defined the public domain prefix "yunikorn.apache.org/" in the scheduler interface.

• https://github.com/apache/yunikorn-scheduler-interface/blob/d472611cf679fc6b2af4e7020af985364ccb6117/lib/go/common/constants.go#L43

To distinguish internal/public metadata usage, we should add an internal domain prefix "internal.yunikorn.apache.org/" to scheduler-interface.