Add OWNERS for packages/Connectivity

In preparation of future modularization of connectivity classes, a large
part of frameworks/base/services/net is planned to be moved to
packages/modules/Connectivity. However moving each class "manually"
to that git project would lose their commit history, and require many
cross-repository topics.

To facilitate the work, create frameworks/base/packages/Connectivity,
which will be used to move the classes at first, before they can all be
moved together with their history to packages/modules/Connectivity. This
mirrors the procedure used for NetworkStack, Tethering,
CaptivePortalLogin, etc. previously.

The added OWNERS file just imports owners from the previous file
location.

Bug: 171540887
Test: m
Change-Id: Ic1c0dbbe8c1f07582c04757ced0ead2fc5b10ca7