Change the shardedNosqlStore to an interface

[jakobht]

What changed?
Added an interface of shardedNosqlStore

Why?
This makes unit testing of nosql_history_store easier

How did you test it?

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

Merging #5893 (a38446b) into master (3e05f2c) will increase coverage by 0.00%.
The diff coverage is 46.66%.

Additional details and impacted files

Files	Coverage Δ
common/persistence/nosql/factory.go	0.00% <ø> (ø)
common/persistence/nosql/nosql_task_store.go	0.00% <ø> (ø)
common/persistence/nosql/nosql_history_store.go	0.00% <0.00%> (ø)
common/persistence/nosql/nosql_shard_store.go	0.00% <0.00%> (ø)
common/persistence/nosql/sharded_nosql_store.go	60.56% <53.84%> (-3.62%)	⬇️

... and 5 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018ec26e-2741-418a-b7de-d459b9ef2fa5

Details

• 8 of 17 (47.06%) changed or added relevant lines in 3 files are covered.
• 31 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.009%) to 67.343%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
common/persistence/nosql/nosql_history_store.go	0	1	0.0%
common/persistence/nosql/nosql_shard_store.go	0	1	0.0%
common/persistence/nosql/sharded_nosql_store.go	8	15	53.33%

Files with Coverage Reduction	New Missed Lines	%
common/task/weighted_round_robin_task_scheduler.go	2	89.05%
service/history/queue/timer_queue_processor_base.go	3	77.82%
service/history/task/transfer_standby_task_executor.go	6	86.6%
service/history/task/task_util.go	20	70.57%

Totals
Change from base Build 018ebfb4-5229-4385-9145-795edac4f8a7:	-0.009%
Covered Lines:	98165
Relevant Lines:	145769

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💛 - Coveralls