Fix _plugin_escalade_rules_only on group assignment

[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

• Linkend to : Improve compatibility with the Escalade plugin moreoptions#9

• Here is a brief description of what this PR does
  The flag was only read by pre_item_update() on Ticket, where escalade sets it on its own internal update to avoid recursion. Callers that assign a technician group themselves (other plugins, scripts) had no way to opt out: a Group_Ticket::add() carrying the flag still went through processAfterAddGroup(), which unassigned the technician when remove_tech is on, forced ticket_last_status and recorded an escalation history entry.

Read the flag in both Group_Ticket hooks so it means the same thing there: escalade skips its logic entirely for that assignment.

Screenshots (if appropriate):

[stonebuzz]

See : pluginsGLPI/moreoptions#9 (comment)