[server] Disable sidebars in Genesis
[server] Disable sidebars in Genesis

Summary:
As described in the previous diff, we want to disable relationship row creation in Genesis. To do this, we need to disable all open subthreads.

The reason for this is that open subthreads end up having `role=0` `memberships` rows for non-members (anybody who has `KNOW_OF`). Since all members of the parent will have `KNOW_OF`, that means any open subthreads that is created (including sidebars) will result in the same pattern of everybody getting a relationship row with everybody else.

Test Plan: Make sure users can't create sidebars anymore after rerunning `soft-launch-migration.js`

Reviewers: palys-swm, atul

Reviewed By: palys-swm

Subscribers: KatPo, Adrian

Differential Revision: https://phabricator.ashoat.com/D1417

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