Add account creation check

Problem/Motivation

It is recommended that only administrators can create new accounts, so setting "Who can register accounts?" to "Administrators only" under /admin/config/people/accounts is good practice.

Steps to reproduce

Proposed resolution

Check if "Who can register accounts?" is set to "Administrators only".

Remaining tasks

Add a new "Account creation" check, which checks if "Who can register accounts?" is set to "Administrators only".

• Title: Account creation
• Review results title: Only administrators can create new accounts.
• Review results path: /admin/reports/security-review/help/security_review/account_creation.
• Review results text: Attackers commonly attempt to register a new account. It is good practice to only allow administrators to create new accounts, see Configuring User Account Settings → .
• Check fail text: Not only administrators can register new accounts.

User interface changes

API changes

Data model changes