Change flushing log to verbose

Lots of logspam while scrolling that impact system performance. So make it default disabled.
To turn on verbose log, use command:
> adb shell device_config put content_capture logging_level 2

Bug: 227352259
Test: atest CtsContentCaptureServiceTestCases
Change-Id: I0044a82be51d1a26ffbb3cf4058f8e7f13e7ebae