feat: this commit introduces the grant enumeration in the domain.concepts namespace to represent different types of grants.

Author: https-richardy

Source/HttpsRichardy.Federation.Domain/Concepts/Grant.cs

@@ -0,0 +1,8 @@
+namespace HttpsRichardy.Federation.Domain.Concepts;
+
+public enum Grant
+{
+    Unspecified,
+    AuthorizationCode,
+    ClientCredentials,
+}