Added eslint rule to prevent usage of new Error()
Added eslint rule to prevent usage of new Error()

- we have our own error library that should always be used to wrap errors in useful info
- therefore instead of new Error() we should always be using errors.SomeError from @tryghost/error

TryGhost/Ghost,janvt/Ghost,janvt/Ghost,TryGhost/Ghost,ErisDS/Ghost,ErisDS/Ghost,ErisDS/Ghost,TryGhost/Ghost,e10/Ghost,e10/Ghost