Create `notify` stage post-prod deploy
- We should correctly mark the stage
prod_deploy
as successful once Capistrano has finished, instead of blocking it / marking it as unsuccessful if notifications fail, as they're a post-deploy action -
rake notify
requires source checkout, as theRakefile
isn't embedded into the image - Therefore we should have a separate stage for performing notifications post-deploy
Found as part of failed merges following !102 (merged).