Start/end sync signals

[adorton-adobe]

Summary

• GOAL: send start and and sync signals for each UMAPI target (send start on first batch and end on last batch)
• Refactor user updates (new users, user updates, group changes, and adobe-only users) so we can identify start and end of each batch per UMAPI target
• Primary target in separate list from secondary targets so we can execute secondary workflows before the primary
• Update logging to reflect new workflow

Testing Steps

• Run a test sync with more than 10 new or updated users
• The log contains new messages to indicate when the signals are sent
• All basic workflows (plus multi-target) are tested, but we still need to test Adobe-only edge cases such as exclude or write-file

Fixes #722

[Luci2015]

if one would keyboard interrupt the process (or get any unhandled exception during the sync), the end signal is not sent and have to wait for the 30min-60min timeout on next run?

[adorton-adobe]

I believe it would revert to default throttling behavior. I will bring this up in my next meeting with the platform team.