Allow decoding thrift from base64 string via CLI

[vytautas-karpavicius]

What changed?
Added additional option to decode Thrift data structure from base64 string (instead of hex encoded).

Why?
Encoded thrift payload is often represented as base64 string (instead of hex). This will allow decoding such strings easier.

How did you test it?
Tried running ./cadence admin db decode_thrift -enc base64 -i ...

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 1ce9595e-ad04-40b4-ba07-d7d50494df07

• 0 of 13 (0.0%) changed or added relevant lines in 1 file are covered.
• 128 unchanged lines in 15 files lost coverage.
• Overall coverage decreased (-0.07%) to 56.951%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tools/cli/adminDBCleanCommand.go	0	13	0.0%

Files with Coverage Reduction	New Missed Lines	%
common/types/shared.go	1	26.66%
service/history/execution/mutable_state_task_refresher.go	1	73.58%
common/task/weightedRoundRobinTaskScheduler.go	2	89.64%
service/history/execution/mutable_state_builder.go	2	69.63%
service/history/task/transfer_active_task_executor.go	2	71.93%
common/persistence/serialization/parser.go	4	65.41%
common/persistence/serialization/thrift_decoder.go	4	61.22%
common/types/mapper/thrift/shared.go	4	63.9%
service/history/task/transfer_standby_task_executor.go	6	88.65%
common/persistence/sql/workflowStateMaps.go	11	85.56%

Totals
Change from base Build 1f10f645-572a-4398-b880-345743744844:	-0.07%
Covered Lines:	83898
Relevant Lines:	147316

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💛 - Coveralls