API name change - from RegionUserCount to RegionDeviceCount

[chinaunicomyangfan]

Problem description
The naming of the Region User Count project does not match the actual functionality of the API

Possible evolution
After discussion in RUC work group, we believe that switch the API name from RegionUserCount to RegionDeviceCount is more accurate because operators can count the number of connected devices rather than the number of users. Specific discussions can refer to camaraproject/RegionDeviceCount#8

Alternative solution
Maybe RegionSimCount is more accurate,but I think it is too technical and not easy to understand

PR is here