Payment confirmation emails refer to Codidact #1892
Description
Describe the bug
When a donation is made, the email confirming that it was successful links to Codidact.
Expected behavior
This email should either not link to anywhere, and just be a generic wording, or should pick up a variable so that other instances send emails linking to their instance rather than to Codidact.
Additional context
I'm raising this since it was noticed in the comments on a pull request for which fixing it would be out of scope, so it doesn't get forgotten: #1888 (comment)