Allow adding hooks without depending on an external service

[ozkatz]

It may look like many lines of code, but this is mostly due to vendoring (and internally forking) shopify/goluago.

A detailed proposal, including user story is under design/open/zero-deployment-hooks.md

[nopcoder]

• Think it would have been easy to have the proposal and the code in two different PRs.
• github.com/Shopify/goluago was added to go.mod there is no need to add the code also to our repository
• Instead of calling the server wrapping the controller on the server will have the same effect - just settings the current user on the context and all the rest should be the same.
• Do you prefer to take the code as an experiment and tune it on a different PR (after you disable the lua action type)?

General note about the mechanicam - a lot of systems uses Lua as the engine to drive the hooks - so instead of having a set of yaml files trigger set of lua files, like in neovim you have init.lua and all the reset are functions and events you register to triggered by the system. By leverage the lua runtime and registering the right functions the user can build a complete DAG or a system using Lua - have single or multiple steps in parallel or in serial. No more compile time to register new hooks - you can have the current hooks system implemented in lua. (hope I was clear on what I was trying to suggest here)

[nopcoder]

Excited experiment