Add config for client-side traffic stats rate-limit cache.

This is a no-op change since the config is not used yet, and
the feature flag will be gradually rolled out instead of enabled
by default.
However, this change is necessary for follow-up changes to enable
toggling the feature and configuring its behavior through device
configuration flags.

This change includes:

 1. Disable the service-side cache flag if the client-side flag
    is enabled.
 2. Since the apps don't have enough permission to check the
    feature flag from DeviceConfig. Provides a binder interface
    for returning per-UID config,
    which only returns cache enabled if the SDK level is V+
    or the app's target SDK is V+.

Test: atest FrameworksNetTests:android.net.connectivity.android.net.TrafficStatsTest \
      FrameworksNetTests:android.net.connectivity.com.android.server.net.NetworkStatsServiceTest \
      CtsNetTestCases:android.net.cts.NetworkStatsBinderTest \
      FrameworksNetIntegrationTests:com.android.server.net.integrationtests.NetworkStatsIntegrationTest
Bug: 343260158
Change-Id: Id9761e4aea65fabe6466c875b787e178317a1da2
5 files changed