pallet macro: Tasks doesn't support instantiable pallets.

[gui1117]

The code only handles non instantiable pallets like this:

				impl<T: Config> core::fmt::Debug for #ident<#type_use_generics> {
					fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
						f.debug_struct(stringify!(#ident)).field("value", self).finish()
					}
				}

[ggwpez]

cc @gupnik

[gui1117]

I have an initial implementation here: https://github.com/paritytech/polkadot-sdk/compare/master...gui1117:gui-tasks-instantiable-pallets?expand=1