Cannot differentiate between an inexistant and an unfinished execution

**Describe the bug**
When checking an execution quality status, it is not possible to differentiate between an inexistant execution (via job url) and unfinished execution. In both case, the response is `STILL_COMPUTING`. This is misleading.

**To Reproduce**
Steps to reproduce the behavior:
1. Open your ARA Swagger
2. Go to `execution-resource`
3. Go to `GET` `/api/projects/{projectCode}/executions/quality-status` (`getQualityStatus`)
4. In the `projectCode` field, type a **valid** project code but an **invalid** url in the `jobUrl` field

**Expected behavior**
Inexistant executions should return a different status, such as `UNKNOWN`.

**Screenshots**