[Request] Add list subcommand to list dimensions

[Aareon]

I've found that after creating a new dimension, then restarting the server, DimLib does not register dimensions it has created or are present. This forces the server owner to re-execute add_dimension to register the dimension again. DimLib should register all dimensions it has created previously at launch and offer a list using the subcommand list

[qouteall]

"DimLib does not register dimensions it has created or are present" seem to be a bug. Opened another issue for it #3

[qouteall]

Did you correctly register the codec of chunk generator? Not registering codec cause the dimension to vanish after server restart.