Feature request: Metadata sanitize function

[hannahilea]

(Initially raised by @palday)
In cases where metadata may contain private information (e.g., schema names; package names etc. when #46 is implemented), it would be helpful to allow these values to be stripped before sharing with consumers who should not have access to that info.

[jrevels]

I think this is achieved just by not using Legolas.write (and instead using w/e method you want, e.g. Arrow.write)?

so probably don't want to add any actual functionality here but can just document it / call it out in tour.jl