[PASSPOINT] Add metrics to determine deployment/avail of Passpoint

Add metrics which will help determine Passpoint availability in the
wild. The metrics measure the percentage of time a Passpoint network
is visible to user - by collecting historgrams of observations per
scan result.

(cherry-pick of commit 9831c1a04929d8d2cadbebbc1e6843895653bd4c)

Bug: 66951771
Test: unit test
Change-Id: I80af113f120515d86b2b6adb3e44ce37e97d5441
Merged-In: I51e05e9a075259544008107810c4489e8111cfcd
2 files changed