Redirect french PDF pages to firefox.com (#16395)

[janriokrause]

Redirect french PDF pages to firefox.com

Testing:

$ curl --silent --head "http://localhost:8000/fr/firefox/features/free-pdf-editor/" | grep -E "HTTP|location"
HTTP/1.1 301 Moved Permanently
location: https://www.firefox.com/fr/features/free-pdf-editor/?redirect_source=mozilla-org

$ curl --silent --head "http://localhost:8000/fr/firefox/features/complete-pdf/" | grep -E "HTTP|location"
HTTP/1.1 301 Moved Permanently
location: https://www.firefox.com/fr/features/complete-pdf/?redirect_source=mozilla-org

[stevejalim]

R+

Thanks for the contribution @janriokrause - it will be in production with the next release, either today or tomorrow

[stevejalim]

@janriokrause Actually, before I merge this, would you mind adding a couple of tests? The easiest way is to expand the current coverage by adding some new test params - here's an example of a different page being tested https://github.com/mozilla/bedrock/blob/main/bedrock/firefox/tests/test_redirects.py#L290-L295 and you can run file with pytest -k test_redirects.py

[janriokrause]

Sure, thanks for the hints.