Add Event to MergeTree and Sequence on Local Segment Op Ack

[anthony-murphy]

Emit a new maintenance event, ACKNOWLEDGED when the op is round tripped from the server and the local segment is ack

[anthony-murphy]

@montselozanod who i can't add as a reviewer for some reason

[anthony-murphy]

/azp run Build - client packages

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[DLehenbauer]

The failed test just needs to be taught to expect ACKNOWLEDGEMENT (-4) events. :-)

Change looks good.

[msfluid-bot]

■ @fluidframework/base-host: No change

Metric Name	Baseline Size	Compare Size	Size Diff
main.js	169.41 KB	169.41 KB	■ No change
Total Size	169.41 KB	169.41 KB	■ No change

⯅ @fluid-example/bundle-size-tests: +332 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
container.js	193.96 KB	193.96 KB	■ No change
map.js	45.92 KB	45.92 KB	■ No change
matrix.js	144.44 KB	144.59 KB	⯅ +155 Bytes
odspDriver.js	195.89 KB	195.89 KB	■ No change
sharedString.js	158.48 KB	158.65 KB	⯅ +177 Bytes
Total Size	738.69 KB	739.01 KB	⯅ +332 Bytes

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Baseline commit: 1329424

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