Rudder

We are bumping Rudder version to 4.0 in master because:

- next major will be 4.0, not 3.3 (major changes, among them Policy Mode: Verify, + bunch of incompatibles changes in packaging, initial promise management, etc)
- if we need to release a Rudder 3.3 for some reason before 4.0, it is impossible to fork it from master, due to the previously depicted changes
- we don't want to wait the last minute to have build and doc with 4.0 everywhere.

This ticket just handle the version bump in Rudder pom. Other tickets will be open as children to change other parts of Rudder.