Add a library for DNS resolver to read bpf maps

The library provides an init function and an API for DNS resolver to
query whether the application is allowed to send DNS query based on BPF
maps settings.

Bug: 288340533
Test: atest dns_helper_unit_test (with test CL)
Change-Id: Ibfb383bfb074da2104a25aa4f04ebc32b22d11da