Change privacy policy to be rendered in web UI, add REST API (#19310)

Source string no longer localized, Markdown instead of raw HTML

config/i18n-tasks.yml

@@ -40,7 +40,6 @@ ignore_missing:
   - 'errors.messages.*'
   - 'activerecord.errors.models.doorkeeper/*'
   - 'sessions.{browsers,platforms}.*'
-  - 'terms.body_html'
   - 'application_mailer.salutation'
   - 'errors.500'
   - 'auth.providers.*'