[Admin] Avoid polluting `SolidusAdmin` namespace with components

[waiting-for-dev]

As we'll have many components, it's good if they are not defined without any apparent pattern within modules under the SolidusAdmin namespace. E.g., we could have a SolidusAdmin::OrdersManagament::Component component, but there are chances that a module in any other place could also want a SolidusAdmin::OrdersManagement name. We have talked about defining modules within SolidusAdmin::UI, or we could also establish a ModuleNameComponent convention.