Add integration tests to ensure the privacy pages are always reachable

[stevejalim]

These simple smoke tests ensure that our privacy pages always ultimately return a 200 OK response, even if the client requesting them lacks an Accept-Language header and there is no locale in the actual URL.

(If a bot chooses not to follow a 30x, of course, that's up to them)

Issue / Bugzilla link

Resolves #11979

Testing

To test this work:

• [ ] ./manage.py update_legal_docs to get the latest legal docs in your DB
• [ ] pytest --base-url http://localhost:8000 -k test_privacy_policies_always_200_OK

Integration tests: https://gitlab.com/mozmeao/bedrock/-/pipelines/608753948 + linked www-config run

[stevejalim]

@pmac Refactored and expanded - tests running but OK to take a look now i think

[stevejalim]

Yeap - https://gitlab.com/mozmeao/www-config/-/jobs/2837843560 shows the new privacy-page tests passing in headless integration mode 👍