Serialized missing settings from portal site data
Serialized missing settings from portal site data

refs https://github.com/TryGhost/Team/issues/1599

- old settings `allow_self_signup` and `is_stripe_configured` and `member_signup_access` are now removed in site data, and are replaced by new settings.
- this change maps the new settings to old settings so Portal behavior remains the same
- long term, we'll update usages in Portal to rely on new settings only

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