Re-add grace period to Upload completer for backwards compatibility.

[Joerger]

Fixes backwards compatibility issues that came from #11551

Specifically, If a node starts a session recording in proxy/sync modes (which records the session directly on the Proxy/Auth servers), then the upload completer in the Proxy/Auth services will periodically check for a corresponding SessionTracker for any uncompleted uploads on disk.

Since pre-v9 sessions do not create session trackers for ongoing sessions, the Proxy/Auth servers will incorrectly assume that their uploads are abandoned. As a result, the upload will be completed prematurely and result in an error in the session due to the audit writer being closed on Proxy/Auth side.

Changes:

• Re-add grace period to Upload completer for backwards compatibility.
• Provide grace period to upload completer in Proxy and Auth services so that proxy/sync recording works with old nodes.
• Further decouple uploader from upload completer so that they can be configured as standalone processes more easily.

TODO: manually test and fix any failing tests

[ibeckermayer]

@zmb3 do we have a similar thing in windows_desktop_service? It seems all the other major feature services are changed here but ours.

[zmb3]

@zmb3 do we have a similar thing in windows_desktop_service? It seems all the other major feature services are changed here but ours.

You know now that you say this, we might a long-standing bug that the upload completer will not run if you run a standalone desktop service!

[ibeckermayer]

Straining to wrap my head around an unfamiliar part of the code and so could well be wrong, but may have found a logic bug in the change to checkUploads.

[probakowski]

LGTM