Improve the pre-flight script

[jonasraoni]

Problem
At this moment we have a single pre-flight script that runs at major upgrades.

• It might feel difficult to understand from where the checks are coming without adding comments (e.g. @see: #issue-number)
• Minor upgrades might also have pre-flight requirements, which would save the end user from re-running upgrades.

Possible Solution

• Move the pre-flight check to its underlying migration. The migration class can implement a preflight interface.
• The upgrade code must check which are the appliable migrations and run the pre-flight check for each one that implements the interface.