fix: Add getter and setter for grant_type

src/keycloak/openid_connection.py

@@ -156,6 +156,19 @@ class KeycloakOpenIDConnection(ConnectionManager):
     def server_url(self, value):
         self.base_url = value
 
+    @property
+    def grant_type(self):
+        """Get grant type.
+
+        :returns: Grant type
+        :rtype: str
+        """
+        return self._grant_type
+
+    @grant_type.setter
+    def grant_type(self, value):
+        self._grant_type = value
+
     @property
     def realm_name(self):
         """Get realm name.