I found the solution. In fact add-ons are not made for this. The way to go is just packaging my controller as a jar.
After, I just need to add the dependency to the pom.xml and edit the web-mvc.xml to add :
Code:
<context:component-scan base-package="org.exoplatform.spring.monitoring" use-default-filters="false">
<context:include-filter expression="org.springframework.stereotype.Controller" type="annotation"/>
</context:component-scan>
The only use of creating an add-on would be to have a command to install this into a roo project.