Add an optional flush period

[ppoliani]

Sometimes the sink might not accumulate the buffer size for a long time. In cases like that, it would be nice to flush the buffer withtin a specific time period
and push the values to the subscribers

[coveralls]

Pull Request Test Coverage Report for Build 138

• 8 of 8 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 97.241%

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Totals
Change from base Build 132:	-0.5%
Covered Lines:	94
Relevant Lines:	96

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💛 - Coveralls