Archive Discord #help threads in a search-indexed fashion

Discord help threads are ephemeral, but remain extremely popular as a method to get help.

We could archive these threads in a search-indexed fashion using [linen.dev](https://www.linen.dev/) or one of their competitors.

## Possible Pros

- makes common questions and answers discoverable via search engines
- boosts Bevy's SEO rank by providing tons of valuable content that we can host

## Possible Cons

- mild violation of privacy: by default, names and content of #help will be posted online
- help threads are generally quite casual; they often contain poorly formed questions and off-the-cuff answer. This would not be the "highly curated Q&A" of Stack Overflow
- answers for old Bevy versions will be archived online, which may mislead users. This is particularly bad because our rate of breaking changes is extremely high
- what happens if and when the service we're using to do this goes out of business, or starts charging a non-trivial fee?

## Open Questions

- ~~Github Discussions similarly do not seem to be indexed. Do we want a similar or integrated solution?~~ Edit: these are indexed fine.
- do we want to censor names of users completely? This should be feasible, but reduces the credit granted
- do we want to allow users to opt-out of having their name shared? Of having their
- How exactly does Linen handle threads? Will they be able to support the new forum features?