Fixes #16133: Missing diffDisplayer service in 6.0

[fanf]

https://issues.rudder.io/issues/16133

[Normation-Quality-Assistant]

This PR breaks qa-test

-- stdout -- 
Branch 'branches/rudder/6.0' set up to track remote branch 'branches/rudder/6.0' from 'NRM'.
Your branch is up to date with 'NRM/branches/rudder/6.0'.
Already up to date.
Your branch is up to date with 'NRM/branches/rudder/6.0'.
[...]
Switched to a new branch '6.0_test'
+ '[' --merge = --rust ']'
+ '[' --merge = --scala ']'
+ webapp/sources/rudder/rudder-core/src/test/resources/hooks.d/test-hooks.sh
+ export PYTHONPATH=./relay/sources/rudder-pkg/lib/rudder-pkg/:./relay/sources/rudder-pkg/lib:
+ PYTHONPATH=./relay/sources/rudder-pkg/lib/rudder-pkg/:./relay/sources/rudder-pkg/lib:
+ find . '!' -name convertOpenLDAPSchema.py -name '*.py'
+ xargs pylint -E --persistent=n --disable=C,R,import-error,no-member,no-name-in-module
No config file found, using default configuration

You should run ./qa-test in your repository to make sure it works.
You can also run rudder-dev merge https://github.com/Normation/rudder/pull/2573 --test to test with upmerging.
After this, you can remove the qa: Can't merge ta
-- Your faithful QA (https://ci.normation.com/jenkins/job/merge-accepted-pr/16775/console)

[fanf]

OK, squash merging this PR