Add latch mechanism to pause/resume in inmemory source

[pcnfernando]

Purpose

Fixes #1603

[codecov-io]

Codecov Report

Merging #1605 into master will decrease coverage by 0.01%.
The diff coverage is 86.66%.

@@             Coverage Diff              @@
##             master    #1605      +/-   ##
============================================
- Coverage     67.87%   67.85%   -0.02%     
  Complexity       45       45              
============================================
  Files           654      654              
  Lines         27982    27995      +13     
  Branches       4403     4405       +2     
============================================
+ Hits          18993    18997       +4     
- Misses         7158     7167       +9     
  Partials       1831     1831

Impacted Files	Coverage Δ	Complexity Δ
...iddhi/core/stream/input/source/InMemorySource.java	93.93% <86.66%> (+13.93%)	0 <0> (ø)	⬇️
.../siddhi/core/util/event/handler/StreamHandler.java	62% <0%> (-12%)	0% <0%> (ø)
...siddhi/core/util/IncrementalTimeConverterUtil.java	52.77% <0%> (-5.56%)	0% <0%> (ø)
.../processor/stream/window/DelayWindowProcessor.java	78.18% <0%> (-5.46%)	0% <0%> (ø)
...ut/stream/state/AbsentStreamPreStateProcessor.java	82.11% <0%> (-1.33%)	0% <0%> (ø)
.../io/siddhi/core/util/snapshot/SnapshotService.java	70.8% <0%> (+0.2%)	0% <0%> (ø)	⬇️
...o/siddhi/core/aggregation/IncrementalExecutor.java	81.25% <0%> (+0.78%)	0% <0%> (ø)	⬇️
...ore/util/persistence/InMemoryPersistenceStore.java	58.97% <0%> (+5.12%)	0% <0%> (ø)	⬇️

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