Bug 1811537 - Add secret setting allowing to overwrite the `country` and `city` parameters for Pocket sponsored stories

[Alexandru2909]

For 1811537 - Add secret setting allowing to overwrite the country and city parameters for Pocket sponsored stories.

https://user-images.githubusercontent.com/35462038/217459793-4f3cd12f-1e1f-4260-9868-21b94b83c372.mp4

Pull Request checklist

• [ ] Tests: This PR includes thorough tests or an explanation of why it does not
• [x] Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• [ ] Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

QA

• [x] QA Needed

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GitHub Automation

Fixes #28791

[gabrielluong]

@Alexandru2909 Please use the correct format for the Bugzilla issues in your PR title and commit message otherwise they won't be linked to Bugzilla: Bug xxxxxx -.

The Bugzilla/GitHub integration is only ran once when you open your PR. You'll need to manually link this PR to the Bugzilla issue.

[Mugurell]

Could we put the new settings in a separate menu maybe similar to the "HTTPs-Only Mode" one? Going by the video, as an outside user the screen becomes a bit bloated so a separate menu could help with this and also make the correlation between Site parameter / City parameter and the Pocket sponsored stories feature clearer.

[mergify[bot]]

This pull request has conflicts when rebasing. Could you fix it @Alexandru2909? 🙏