Update Discord link to new dedicated URL

[Ethan-Arrowood]

https://harper.fast/discord is now a proper redirect established for our Discord community so we should updated any discord links to use this new one instead. I think there are a couple places in the docs to update this (such as the footer). But as a side note we should also updated this in the GitHub organization header and other meta docs too.

[Ethan-Arrowood]

I update the link on the GitHub org and across some metadata files; still need to make the change within this repo.