Replace "free access" logic with "requires add-on"

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The following discussion from !195765 (merged) should be addressed:

• @GitLabDuo started a discussion: (+5 comments)

  The inline implementation of service_free_access? duplicates the logic that was previously in the free_access? method. This creates code duplication and potential maintenance issues.

          return denied_response unless service.cut_off_date.nil? || service.cut_off_date&.future?

  Consider extracting this logic into a shared module or utility method to avoid duplication across the codebase.

We used to say that a UP/service is in "free access" either when:

• no cut-off date is defined
• this date is in the future

However, this leads to the situation now that by default, everything is in free access unless you define this date, which is unsafe and usually not the case. We should instead base this on the presence of add_ons instead.