Slack link leads to unknown channel when not already joined

Created by: absoludity

Impacted sections

All pages - the slack icon/link is in the header .

Issue Description

The slack icon in the website header links to: https://app.slack.com/client/T1P59QFMF/C05R8DD2AKZ which requires first joining. If you've not yet joined, you'll see:

Perhaps the link should be an invitation link rather than a link to a channel like that used on the main page to join the slack channel. Note that a slack invite link will automatically redirect to the main page if the person has already joined (it's just a bit slower).