Long poll completion buffer to prevent timeouts

[vytautas-karpavicius]

What changed?
Leave some long poll completion room on the server side.
When little time is left until expiration we reserve some time longPollCompletionBuffer when creating a timer to return earlier, so that this request will be able to finish without timeout.
This PR comes with companion client PR cadence-workflow/cadence-go-client#1123. Which will prevent doing additional request all together when too little time is left.
If an older client is used, we still need a safeguard timeout error. Otherwise client would be stuck in long poll loop for the duration of completion buffer, which can result in additional request being made that return empty responses.

Related previous PR: #3830

Why?
The idea here is to prevent context timeout errors, which affects SLAs and is not truly an error.

How did you test it?
Locally. With go client changes and without go client changes.

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 04d2b3e7-35d2-4c7e-b214-bbee20bad89d

• 13 of 17 (76.47%) changed or added relevant lines in 1 file are covered.
• 115 unchanged lines in 13 files lost coverage.
• Overall coverage decreased (-0.06%) to 56.397%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
service/history/historyEngine.go	13	17	76.47%

Files with Coverage Reduction	New Missed Lines	%
client/history/client.go	2	41.25%
client/history/metricClient.go	2	47.05%
common/types/mapper/thrift/shared.go	2	64.98%
service/history/handler.go	2	48.15%
common/persistence/executionManager.go	4	75.5%
common/persistence/statsComputer.go	4	95.71%
service/frontend/workflowHandler.go	4	58.8%
service/history/queue/timer_queue_processor_base.go	4	78.78%
service/history/historyEngine.go	9	70.09%
common/persistence/sql/sqlExecutionStore.go	16	60.0%

Totals
Change from base Build 35aee8df-b422-435f-99b8-dad5f592c3ae:	-0.06%
Covered Lines:	79064
Relevant Lines:	140191

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💛 - Coveralls