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: I3cfbd2f79e71df6b2952d73d5a2bd20268708129
(cherry picked from commit c3249a87)
Merged-In: I3cfbd2f79e71df6b2952d73d5a2bd20268708129