Warn/error on unecessary config items in publishConfig

[wraithgar]

Part of the config validation warning effort #934

[ljharb]

This will be pretty disruptive fwiw - I have ignore in my publishConfig in all my projects, because i use it with https://npmjs.com/npmignore to autogenerate an .npmignore file.

[wraithgar]

Well that's the danger you run when you co-opt a config meant for npm itself.

[ljharb]

That's certainly a position to take, but since npm's never claimed that section as "for itself" before, I'm not sure it's a valuable tradeoff to assert that claim now.

Warning on something that someone might think npm would use, but it doesn't, makes perfect sense - but npm's never warned on any unknown properties before either afaik.