add workflow cleaner to clean expired workflows periodically

[kensou97]

Hi, I ran into a problem while using redis persistence, which has already been discussed in some issues like #1315. Redis memory usage kept growing and random data including some metadata got evicted.
So I add a workflow cleaner in RedisExecutionDAO. It records the timestamp and workflowId in zset (timestamp as score, workflowId as value) when a workflow is created. A background thread will find and clean the expired workflows (indicated by config workflow.cleaner.expire.seconds) periodically. The period is indicated by config workflow.cleaner.period.seconds. If there are too many expired workflows, cleaner will process them batch by batch. The batch size is indicated by config workflow.cleaner.batch.size.
The cleaner is not meant to clean data in IndexDAO or other db implementation, because the disk-based storage may not have this problem. It works well in my environment and I hope this would help someone else.

[coveralls]

Pull Request Test Coverage Report for Build 3887

• 15 of 35 (42.86%) changed or added relevant lines in 2 files are covered.
• 16 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 68.786%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
redis-persistence/src/main/java/com/netflix/conductor/dao/dynomite/RedisExecutionDAO.java	12	32	37.5%

Files with Coverage Reduction	New Missed Lines	%
cassandra-persistence/src/main/java/com/netflix/conductor/dao/cassandra/CassandraEventHandlerDAO.java	8	69.86%
cassandra-persistence/src/main/java/com/netflix/conductor/dao/cassandra/CassandraMetadataDAO.java	8	55.79%

Totals
Change from base Build 3882:	-0.2%
Covered Lines:	11393
Relevant Lines:	16563

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💛 - Coveralls

[codecov]

Codecov Report

Merging #1609 into dev will decrease coverage by 0.14%.
The diff coverage is 42.85%.

@@             Coverage Diff              @@
##                dev    #1609      +/-   ##
============================================
- Coverage     64.08%   63.93%   -0.15%     
- Complexity     3424     3429       +5     
============================================
  Files           273      273              
  Lines         16217    16252      +35     
  Branches       1448     1451       +3     
============================================
- Hits          10392    10391       -1     
- Misses         5104     5140      +36     
  Partials        721      721

Impacted Files	Coverage Δ	Complexity Δ
...m/netflix/conductor/core/config/Configuration.java	71.42% <100%> (+3.42%)	15 <3> (+3)	⬆️
...flix/conductor/dao/dynomite/RedisExecutionDAO.java	72.25% <37.5%> (-3.76%)	61 <2> (+2)
...ductor/dao/cassandra/CassandraEventHandlerDAO.java	68.49% <0%> (-10.96%)	15% <0%> (ø)
.../conductor/dao/cassandra/CassandraMetadataDAO.java	54.73% <0%> (-4.22%)	24% <0%> (ø)

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