introduce modularity in our playbooks

[lunika]

Purpose

In #175 we want to execute a task depending on a context and specific to an app. So we need to be able to execute tasks that are "application centric".

Proposal

Create a "hook" system. Tasks can live in the application folder and will be executed if they follow a pattern we choose. You should create a hooks folder and then in it files with the name of the hook you want to implement. For example for the hook vaults_created you should create this file for the forum application: apps/forum/hooks/vaults_created.yml

• [x] create tasks to execute hooks
• [x] example how to use them

[jmaupetit]

I like the idea, but I think we must talk a bit more of what must be achieved first. This implies dependencies between applications. IMO that should be implemented first.

[lunika]

This PR is a POC and I'm open to discuss about what can be implemented