Merge branch '21569-dont-add-created-by-for-matched-users' into 'master'

Only add original author tag line when importing from GitHub if there isn't a linked GitLab account

## What does this MR do?
If there we've found a linked GitLab user for a creator of an issue or comment don't add the 'Created By:' line.

## What are the relevant issue numbers?

Closes #21569

See merge request !6081