Allow for parament threads

I am loving the new threads system, but I feel like admins/mods should be able to make permanent threads. By doing so, the function would allow servers to set up discussions people can opt-in and out of at any time rather than having to use roles and role bots!

Some good examples this could be used for:
Spoilers!
People who play certain types of games
Opt into different topics
Removes the need for role bots for people to opt into a topic which don't always work
and many more that I can't think of but sure other communities could make use of

Also, PLEASE don't lock this behind server boosts.