fix(plugin-meetings): send metric when whiteboard share is stopped

[jor-row]

COMPLETES SPARK-705847

https://jira-eng-gpk2.cisco.com/jira/browse/SPARK-705847

Currently on web app when whiteboards are stopped the client.share.stopped ca event is not sent. This is because Web app does not utilise stopWhiteboardShare from the sdk for warhol whiteboards where this event is currently sent. Using this function causes some duplicate requests to be made, and one conflicts, so I'm not going to mess with the implementation and just add the metric to be sent when we get the locus media event that whiteboard share has stopped.

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