Post deploy hooks

[ato]

Some people want to run scripts post-deploy. For example:

• Moving static assets around
• Restarting dependent processes
• Triggering database migrations

Sometimes they abuse nla-deploy.sh to try to do these things. It usually ends in tears.

We maybe should support something like this officially but it's not clear to me exactly how the feature should work.

[brycollins]

What about having another script in the repo that is executed after deploy if it exists, e.g nla_post.sh