Don't count proxied jobs toward scheduling limit.

1. Some API calls (such as SyncManager calls) can result in multiple job
schedule calls. Given that underlying implementation detail, we don't
count jobs scheduled via proxy towards the source app's schedule limit.
Calls using scheduleAsPackage for itself will still count.
2. Limit the number of times we log that a specific app has exceeded the
limit to once per minute.
3. Update the error message and documentation to help developers
identify what to do when they encounter the issue.

Bug: 160796417
Test: atest JobSchedulerServiceTest
Test: atest JobSchedulingTest
Test: Run `m offline-sdk-docs` and check page at out/target/common/docs/offline-sdk/reference/android/app/job/JobScheduler.html
Change-Id: Ia682aa889ec2a26d373d0309e8c0324570f7d816