[common/persistence] Add ExecutionManager tests

[3vilhamster]

What changed?
I've introduced tests for proxy methods in persistence/ExecutionManager type.
To achive it I've created mocks for ExecutionStore and PayloadSerializer so that unit tests can focus only on manager logic.
As a first step I only test proxy methods that do not provide any logic. I'll follow up with a PR that focuses on more complex methods.

Why?
To increase code coverage and code quality.

How did you test it?
unit tests

Potential risks
None

Release notes

Documentation Changes

[dkrotx]

stamped with 2 comments

[codecov]

Codecov Report

Merging #5803 (f9041d9) into master (b6cfd48) will increase coverage by 0.08%.
The diff coverage is 100.00%.

Additional details and impacted files

Files	Coverage Δ
common/persistence/data_store_interfaces.go	100.00% <ø> (ø)
common/persistence/execution_manager.go	12.07% <100.00%> (ø)
common/persistence/serializer.go	76.20% <ø> (ø)

... and 2 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018e60e6-74a5-4e89-90ce-79a84a394cc6

Details

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• 44 unchanged lines in 7 files lost coverage.
• Overall coverage increased (+0.04%) to 65.183%

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Files with Coverage Reduction	New Missed Lines	%
common/task/weighted_round_robin_task_scheduler.go	2	88.56%
common/task/fifo_task_scheduler.go	2	85.57%
service/history/execution/mutable_state_util.go	2	78.48%
service/history/task/fetcher.go	4	85.05%
service/matching/taskListManager.go	7	79.7%
service/history/task/transfer_standby_task_executor.go	10	86.6%
service/history/execution/mutable_state_task_refresher.go	17	65.82%

Totals
Change from base Build 018e5de2-13e5-4ee7-8b49-541f9f2abb50:	0.04%
Covered Lines:	95283
Relevant Lines:	146178

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💛 - Coveralls