Add "Enter to Group" property to Make Group operator.

Currently Make Group operator (node.group_make) forces user to enter the group after creating it.

This is not always what users prefer.

It would be good if the operator would have a property to enter the group, or not, after creating the group.

Then we could set that behavior to our preferences. Or, have two hotkeys for creating and entering a group, or just creating it.

It would be trivial to make a script that exits the group after creating it. But I find this would be good to have as a default option in Blender.