Schedule binary measurement job at boot completed.

Instead of waiting until first invocation of commandline,
we are scheduling the computation of SHA256 digest of
APEXs and Modules at post boot such that the job can
be run when the device is idle.

For this purpose, an inner static class that extends
JobServer is created, and a declaration of this service
in the manifest which is protected by BIND_JOB_SERVICE
is also necessary.

This allows the logging of APEX information to statsd
to still happen at least once every reboot (when the
device is idle). Otherwise, logging may never occur
if the users never make use of the commandline.

Bug: 217469982
Test: Manual.
Job is found to be triggered automatically when device
is left overnight.

Job can also be manually triggered (for test) via
`adb shell cmd jobscheduler run android <job_id>`
Job id can be found via printout in logcat after
the scheduling is successfully done.

After job is run, `adb shell cmd transparency
get apex_info` no longer has latency upon first
invocation.

Change-Id: I7cff80d53b37152639bb9aebaca50f5b61733ea7