Fix service level deletion by rule

[Lainow]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes !42563
• Here is a brief description of what this PR does
  When the user has a rule that adds an SLA when creating a ticket, if they have another rule that removes this SLA when deleting a technician group, the latter did not remove the group (whereas it did so without the plugin).
  The reason was that the rules did not trigger ONUPDATE because no field was changed when the group was removed, as removeAssignGroup() deletes the old group directly in SQL, without going through the rules engine.

To correct this, before deleting the old group, we call $ticket->getFromDB() then $ticket->update() with _actors containing only the new group. GLPI then detects the old group as deleted in transformActorsInput(), loadActorsForRules() sees a real change, and the business rules are executed with the correct final state (SLA deleted, etc.). The _plugin_escalade_rules_only flag is passed to prevent re-entry into the escalation logic.

And in pre_item_update, immediate return if _plugin_escalade_rules_only is present, letting prepareInputForUpdate() run the rules and save the results normally.

Screenshots (if appropriate):