Add Android Multiuser Atom which will contain number of supported users.

Metric [Design Doc approved](https://eldar.corp.google.com/assessments/860295929/revisions/1?jsmode=du&mods=eldarui_search#sections/999001).

Bug: 240582354
Test: statsd_testdrive 10160
Change-Id: I6a626738bd6de15d0c73cbf3a72acda8c6f2bac5
(cherry picked from commit b8c49619cfc50fc68631a5b6a1a0cc09bedaa708)
Merged-In: I6a626738bd6de15d0c73cbf3a72acda8c6f2bac5