Add the ability to change the default text of each aggregation stage (and reset to the built-in one).

I would like to be able to, for example, change the default $lookup text so that the string values don't contain spaces (e.g. localField: "fieldfromtheinputdocuments" instead of localField: "<field from the input documents>") so that I can double click to select the entire content of the string, instead of having to delete by hand.

I think that creating templates, instead of just changing the $lookup default, might be a more powerful option.