More robust candidate broadcasting

[robertdstein]

This PR increases robustness/improves fallbacks of candidate broadcasting:

• It extends the timeout window in penquins from default 5s to 600s, for source crossmatching
• It groups sources in batches of 1 for source crossmatching via Kowalski, so that a timeout would affect only a single source table
• It sets a limit of 4 threads for crossmatching API calls, to avoid inadvertent DDOS attacks with 40 threads :sweat_smile:
• It better allows sources to be resent to skyportal via API rather than IPAC. That was possible before, but should now be much closer to normal IPAC-style candidates: annotations are now identical, and all candidates sent via API are marked in the db as sent.
• Adds more flexibility for annotations. Now passed as an argument to skyportal processors, and includes rb score for WINTER.

[coveralls]

Pull Request Test Coverage Report for Build 9136150094

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 11 of 15 (73.33%) changed or added relevant lines in 4 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 84.613%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
mirar/processors/skyportal/skyportal_candidate.py	6	10	60.0%
<!--	Total:	11	15	73.33%	-->

Files with Coverage Reduction	New Missed Lines	%
mirar/processors/sources/source_selector.py	6	58.24%
<!--	Total:	6		-->

Totals
Change from base Build 9103899040:	-0.04%
Covered Lines:	10954
Relevant Lines:	12946

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💛 - Coveralls