apmanager: add init script

Add init script to start apmanager daemon during system startup.

BUG=chromium:442188
TEST=emerge-$BOARD apmanager and manually verify apmanager daemon is
     running after system is restarted.
CQ-DEPEND=CL:235643

Change-Id: Ic6bb018fc41031701cb5f360e2c1c9e37ffe360e
Reviewed-on: https://chromium-review.googlesource.com/235644
Reviewed-by: Peter Qiu <zqiu@chromium.org>
Tested-by: Peter Qiu <zqiu@chromium.org>
Commit-Queue: Peter Qiu <zqiu@chromium.org>
1 file changed