[web][native] add test button to create DM thread

Summary:
This code allows testing DMs on prod for staff. We can create a thread and then using diff from this stack add members and test all DMs features.

Log in/log out erase all DMs data (there is no backup).

Depends on D13199

Test Plan: Check is thread is created

Reviewers: tomek, inka

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13200