Turn on Threads for all users

[gileluard]

Make the threads feature available for all users. The labs flag should persist in order to let the user disable threads.

Depends on element-hq/element-meta#187

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. (see. Turn on Threads for all users (out of labs) #5799)

Have you considered any alternatives?

No response

Additional context

No response