Expose some metadata on makeScripts

[kamadorueda]

For avoding to write code like this: https://gitlab.com/fluidattacks/product/-/blob/98c98731063823affbb14a2cf86c0737f5043a29/makes/foss/units/observes/scheduled/on-aws/code-etl-mirror/main.nix#L19

and instead writting code like this:

outputs."/script".tree.bin

tree represents the contents of $out, and bin the binary to execute