Add system checks to dashboard in admin UI (#15989)

app/lib/admin/system_check/database_schema_check.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class Admin::SystemCheck::DatabaseSchemaCheck < Admin::SystemCheck::BaseCheck
+  def pass?
+    !ActiveRecord::Base.connection.migration_context.needs_migration?
+  end
+
+  def message
+    Admin::SystemCheck::Message.new(:database_schema_check)
+  end
+end