Add unit test for ES v7 client

[neil-xie]

What changed?
Added unit test for ES v7 client, mostly same as v6 client unit test, modified a few paths that are changed in v7

Why?
Test coverage

How did you test it?
Unit test

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 018e1b52-0f43-45fb-b31c-94a0e8274350

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 69 unchanged lines in 12 files lost coverage.
• Overall coverage increased (+0.07%) to 63.343%

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Files with Coverage Reduction	New Missed Lines	%
service/history/queue/timer_queue_processor_base.go	1	77.62%
common/task/parallel_task_processor.go	2	93.06%
common/task/fifo_task_scheduler.go	2	87.63%
common/util.go	2	91.69%
common/persistence/statsComputer.go	3	94.64%
common/asyncworkflow/queue/consumer/default_consumer.go	3	92.05%
service/history/task/transfer_active_task_executor.go	4	72.38%
service/history/task/task_util.go	4	75.14%
service/history/task/fetcher.go	6	85.05%
service/history/task/cross_cluster_task_processor.go	8	80.79%

Totals
Change from base Build 018e1b4e-dbb0-43e9-bc0a-aeb699d11015:	0.07%
Covered Lines:	92859
Relevant Lines:	146598

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💛 - Coveralls

[codecov]

Codecov Report

Merging #5760 (5c64bc1) into master (d1e00cb) will decrease coverage by 0.03%.
Report is 1 commits behind head on master.
The diff coverage is n/a.

❗ Current head 5c64bc1 differs from pull request most recent head 5ed0f3e. Consider uploading reports for the commit 5ed0f3e to get more accurate results

Additional details and impacted files

see 8 files with indirect coverage changes

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