Added validation and moved Unattended Settings into their own model. + Added DataAnnonation validation on all our settings

src/Umbraco.Core/Configuration/Models/Validation/UnattendedSettingsValidator.cs

@@ -0,0 +1,44 @@
+// Copyright (c) Umbraco.
+// See LICENSE for more details.
+
+using Microsoft.Extensions.Options;
+
+namespace Umbraco.Cms.Core.Configuration.Models.Validation
+{
+    /// <summary>
+    /// Validator for configuration representated as <see cref="UnattendedSettings"/>.
+    /// </summary>
+    public class UnattendedSettingsValidator
+        : IValidateOptions<UnattendedSettings>
+    {
+        /// <inheritdoc/>
+        public ValidateOptionsResult Validate(string name, UnattendedSettings options)
+        {
+            if (options.InstallUnattended)
+            {
+                int setValues = 0;
+                if (!string.IsNullOrEmpty(options.UnattendedUserName))
+                {
+                    setValues++;
+                }
+
+                if (!string.IsNullOrEmpty(options.UnattendedUserEmail))
+                {
+                    setValues++;
+                }
+
+                if (!string.IsNullOrEmpty(options.UnattendedUserPassword))
+                {
+                    setValues++;
+                }
+
+                if (0 < setValues && setValues < 3)
+                {
+                    return ValidateOptionsResult.Fail($"Configuration entry {Constants.Configuration.ConfigUnattended} contains invalid values.\nIf any of the {nameof(options.UnattendedUserName)}, {nameof(options.UnattendedUserEmail)}, {nameof(options.UnattendedUserPassword)} are set, all of them are required.");
+                }
+            }
+
+            return ValidateOptionsResult.Success;
+        }
+    }
+}