Closes #6438: Adapt the URL for the job so the SaaS uses the correct one

[Miraeld]

Description

Fixes #6438

Documentation

Technical documentation

We use the function user_trailingslashit when we send the job to the SaaS so the SaaS can use the right URL to proceed and avoid redirections.

Type of change

• Bug fix (non-breaking change which fixes an issue).

Checklists

Feature validation

• I validated all the Acceptance Criteria. If possible, provide sreenshots or videos.
• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I implemented built-in tests to cover the new/changed code.

Code style

• I wrote self-explanatory code about what it does.
• I wrote comments to explain why it does it.
• I named variables and functions explicitely.
• I protected entry points against unexpected inputs.
• I did not introduce unecessary complexity.
• I listed the introduced external dependencies explicitely on the PR.
• I validated the repo-specific guidelines from CONTRIBUTING.md.

[Mai-Saad]

Related test plan https://wpmediaqa.testrail.io/index.php?/runs/view/822&group_by=cases:section_id&group_order=asc

[Miraeld]

I've run tests, here are the results:
testrail-report-579.pdf