Adding guide on how Porter does error handling in CONTRIBUTING.md

[VinozzZ]

adding a note in our release/v1 contributing.md file that addresses how we handle errors in Porter? We could cover the transition from pkg/errors to go standard error wrapping, and also when to wrap an error in general.

[VinozzZ]

the goal for our error handling https://github.com/getporter/porter/issues/2009