Global ratelimiter: client-side Collection skeleton

[Groxx]

A half-fleshed-out skeleton of the quotas.Collection that the frontend will use for these limits,
and a chunk of pseudo-code to show how it'll be used when the RPC PR is ready (coming soon).

This is not completely usable right now and will likely need some small changes, but it has the core bits:

• real limiters / fallbacks / tracking
• dynamically-tweakable background update loop
• logs, metrics, error handling (where reasonable)
• some very simple tests

It will eventually need:

• sharding the limiters by key for all the (relevant) aggregator hosts
• dynamic config to shadow / disable global limiters and control sending update requests.
• swapping the frontend handler's ratelimits to use this instead

[codecov]

Codecov Report

Attention: Patch coverage is 67.36842% with 31 lines in your changes missing coverage. Please review.

Project coverage is 71.99%. Comparing base (b3e21fa) to head (e2b0994).
Report is 1 commits behind head on master.

Additional details and impacted files

Files	Coverage Δ
common/clock/time_source.go	71.42% <ø> (ø)
common/quotas/global/collection/collection.go	67.36% <67.36%> (ø)

... and 12 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018fef57-8f5a-40b9-9c96-fb887e6f92f6

Details

• 94 of 136 (69.12%) changed or added relevant lines in 2 files are covered.
• 23 unchanged lines in 7 files lost coverage.
• Overall coverage increased (+0.04%) to 71.372%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
common/quotas/global/collection/collection.go	86	128	67.19%

Files with Coverage Reduction	New Missed Lines	%
common/cache/lru.go	2	93.01%
service/history/replication/task_processor.go	2	82.76%
service/history/task/transfer_standby_task_executor.go	3	87.55%
service/history/task/task.go	3	84.81%
service/history/queue/timer_queue_processor_base.go	3	77.87%
service/history/handler/handler.go	4	96.14%
service/history/execution/cache.go	6	74.61%

Totals
Change from base Build 018feeec-d7a4-4bb0-b278-1977f0e4c7ed:	0.04%
Covered Lines:	106410
Relevant Lines:	149093

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💛 - Coveralls