Verify accuracy of settings/configuration.md

This is part of https://gitlab.com/gitlab-org/technical-writing/-/issues/936 and is about verifying the accuracy of https://docs.gitlab.com/omnibus/settings/configuration.html.

• Configure the external URL for GitLab
  • Specify the external URL at the time of installation
• Configure a relative URL for GitLab
• Load external configuration file from non-root user
• Read certificate from file
• Store Git data in an alternative directory
• Change the name of the Git user or group
• Specify numeric user and group identifiers
• Disable user and group account management
• Move the home directory for a user
• Disable storage directories management
  • Disable the /etc/gitlab directory management
  • Disable the /var/opt/gitlab directory management
• Start Linux package installation services only after a given file system is mounted
• Configure the runtime directory
• Configure a failed authentication ban
• Disable automatic cache cleaning during installation
• Error Reporting and Logging with Sentry
• Set a Content Delivery Network URL
• Set a Content Security Policy
• Set initial root password on installation
• Set allowed hosts to prevent host header attacks