[notification] Fix sender name in email

[maximemulder]

Brief summary of changes

Display the name of the user instead of their ID in the notification emails.

Testing instructions

1. Trigger an email notification which displays the sender name in the email (such as media file upload).

Link(s) to related issue(s)

• Resolves [notification] Notification email sender name incorrect #9202

[maximemulder]

I still haven't looked at why I get linting errors in files I haven't touched, but I imagine that shouldn't be a blocker ?

EDIT : Surprisingly, the linter seems to be happy here while it was unhappy on my VM 🤔.