Re-aligning GitHub templates. (#7435)
We're moving our feature requests process to Discussions. This PR:
- Creates a template for RFCs in Discussions ([kindly borrowed from
Next.js](https://github.com/vercel/next.js/blob/canary/.github/DISCUSSION_TEMPLATE/ideas.yml))
- Removes the issue template for feature requests
Additionally, I took the opportunity to borrow [the `help.yml` from
Next.js](https://github.com/vercel/next.js/blob/canary/.github/DISCUSSION_TEMPLATE/help.yml)
as it seems like it would help our users out as well.
