Issue #3632720: Add site data-sharing choices to Update Status

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Issue: https://www.drupal.org/project/drupal/issues/3632720

Adds two site owner choices to Update Status: share the site domain name with Drupal.org (checked by default) and share the site email address with the Drupal Association (unchecked by default). Both live in update.settings as nullable booleans; NULL means no choice is recorded. The choice is made on the installer's configure screen for interactive installs, or at Reports > Available updates > Settings, which shows the exact values. Existing sites and non-interactive installs start a 30-day notice period: nothing is sent during it, and a status report warning and an admin page message point to the settings form. After it the defaults apply until a choice is saved. The notice period is isolated in DataSharing::effectiveValue() and the prompts, and can be removed without the rest of it, if desired.

Values are sent once per refresh with the core update check, only to the default Drupal.org endpoint, as one GET to https://updates.drupal.org/site-data. That endpoint does not yet exist; see the issue.

Open in the issue: the domain default, the notice period length, the transport.

To test: install interactively, or update an existing site, then visit the settings page and the status report.