Turn on Threads for all users (out of labs)

[novocaine]

Your use case

Make the threads feature available for all users.

Depends on element-hq/element-meta#187

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We aim to release Threads on 20 December, we will do so by:

• completing testing before the RC and during the RC period (both team, internal, and community)
• defaulting the labs flag to on for users

Once released, we should remove the labs flag with at least one cycle between 20 December and the removal of the switch in product.

[daniellekirkwood]

👀 @justjanne & @gsouquet