Add service 'overlay' to service_contexts

The 'overlay' service is the Overlay Manager Service, which tracks
packages and their Runtime Resource Overlay overlay packages.

Change-Id: I897dea6a32c653d31be88a7b3fc56ee4538cf178
Co-authored-by: Martin Wallgren <martin.wallgren@sonymobile.com>
Signed-off-by: Zoran Jovanovic <zoran.jovanovic@sonymobile.com>
Bug: 31052947
Test: boot the Android framework