[server] Send updates to all the members of parent thread
[server] Send updates to all the members of parent thread

Test Plan: Open two instances of the app, with different users. Send a message to a sidebar and check if thread state was updated on the other device: the replies count should increase.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian, atul, subnub, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D688

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