[feature request] gatsby dry run command

[swyxio]

Summary

add a dry run feature that runs through and logs out each of the lifecycles and plugins being detected and run in turn

• ng cli has a dry run feature
• aws cli has a dry run feature
• rspec has a dry run feature

Basic example

gatsby dryrun

runs the build without actually executing the build

Motivation

we want to debug things cheaply

[swyxio]

some more info on the demand here: https://news.ycombinator.com/item?id=27263136