feat(taskfile): add post tasks feature

[peterparser]

Hi, while using go-task I found that a post-tasks like feature would be cool, in my case it would be nice to use it as a teardown for my test environments.

I used posts as a keyword for implementing this feature, if you find something more suitable I will be more than happy to refactor it.

Thank you!

[andreynering]

Hi @peterparser,

Why do you think posts would be useful?

You can already add extra commands to your cmds list. And to ensure something is run even after a fail, we already have defer.

So, I'm inclined to not have this so we don't have an overlap of features.