Checkin worker for extractors

[toondaey]

This is a more robust implementation of startup/checkin for extractors. The actual code is just about 359 lines here while the other changes are just tests.
This is supposed to help with:

• Ensuring that we either don't report any checkin until a start up has been reported or we only report errors not related to tasks run
• Ensuring that errors and/or task updates are reported chronologically.

It also ensures that a restart of extractors are triggered when the config is changed remotely where the extractor is using a remote config or a fatal error is reported when the extractor encounters an unrecoverable misconfiguration.

The worker also handles chunking of errors/task updates as required by the integrations API.

[codecov]

Codecov Report

❌ Patch coverage is 77.52809% with 40 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.25%. Comparing base (2302bc4) to head (e0cc6c7).

Files with missing lines	Patch %	Lines
...ite/extractorutils/unstable/core/checkin_worker.py	77.52%	40 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #464    +/-   ##
========================================
  Coverage   79.25%   79.25%            
========================================
  Files          42       43     +1     
  Lines        3692     3866   +174     
========================================
+ Hits         2926     3064   +138     
- Misses        766      802    +36     

Files with missing lines	Coverage Δ
...ite/extractorutils/unstable/core/checkin_worker.py	77.52% <77.52%> (ø)

... and 3 files with indirect coverage changes

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[einarmo]

This looks pretty good. I think some explanatory comments in the complex parts may be good, and I have some concerns around the locks, but it's taking shape. You will probably need a size exemption.