issue #12450: return original URL in original_url JSON field

[eric-belhomme]

As related in issue #12450, the field original_url is always empty when requesting the API route GET repos/{orga}/{project}, even when the project is a mirror repo.

In such case I would excpect to get in original_url the URL of the origin repository used to initiate the project.

This PR is my attempt to fix this :

curl -s -X GET "http://127.0.0.1:3000/api/v1/repos/rico/input-event-daemon?access_token=$TOKKEN" -H "accept: application/json" | jq
{
  "id": 1,
...
  "html_url": "http://localhost:3000/rico/input-event-daemon",
  "ssh_url": "rico@localhost:rico/input-event-daemon.git",
  "clone_url": "http://localhost:3000/rico/input-event-daemon.git",
  "original_url": "https://github.com/eric-belhomme/input-event-daemon.git",
 ...
}

I tested my patch with mysql and sqlite3 database backends with no errors.

[6543]

ping

[6543]

Backport: #13886