Moves what is possible for identity back office to Core, configures backoffice identity with IOptions and our password settings

src/Umbraco.Core/BackOffice/BackOfficeUserPasswordCheckerResult.cs

@@ -0,0 +1,12 @@
+namespace Umbraco.Core.BackOffice
+{
+    /// <summary>
+    /// The result returned from the IBackOfficeUserPasswordChecker
+    /// </summary>
+    public enum BackOfficeUserPasswordCheckerResult
+    {
+        ValidCredentials,
+        InvalidCredentials,
+        FallbackToDefaultChecker
+    }
+}