DrmManager: locally aggregate API metrics

Aggregate DrmManager API invocation counts per plugin over at least
fixed period of time before sending metrics to mediametrics service.

The default period is 1 day; the period is configurable through the
property drmmanager.metrics.period.

Bug: 134789967
Test: dumpsys media.metrics
Change-Id: I2cf28f1dfaa485ca319360705b872eed995b3d7f