Matches the URL content by regular expression

This patch provides a way to configure the regular expression
which is used for matching the URL content. Once the result is
matching, then NetworkMonitor will treat the validation result
as fail or success.

Bug: 141406258
Test: 1. Build pass
      2. atest NetworkStackTests

Change-Id: I77747b34fad895565d42ea4c017759c256d61489