[VCN13] Implement tracking best matching network

This is done by:
  1. In requestNetwork, provide a basic permission check.
  2. rematchNetworksAndRequests: no change, since non listen
     requests will be automatically processed to track
     best satisfying network.
  3. applyNetworkReassignment: no change, since non-request
     will not be sent to factories.

Test: atest ConnectivityServiceTest#testRegisterBestMatchingNetworkCallback_noIssueToFactory
Test: atest ConnectivityServiceTest#testRegisterBestMatchingNetworkCallback_trackBestNetwork
Bug: 175662146
Change-Id: I8cf4ab334df6812d84cdda160e9b72b6f54062af