docs: add script for unlisting array of forms

[mantariksh]

Problem

Unlisting several forms at once is a common database operation which can take prohibitively long if there are many (e.g. hundreds) of forms to unlist at once.

Solution

Add a function to our MongoDB scripts which unlists an array of form IDs. Since the forms to unlist are often given as form links and not object IDs, include a parsing step so any string can be passed into the function as an array element, as long as it contains the form ID.

[mantariksh]

@syan-syan requesting your review to make sure this fits your needs!

[karrui]

lgtm