feat: add activity message for SLA (#9100)

* feat: add activity message for SLA

* chore: refactor to reduce method complexity

* chore: refactor

* feat: add spec for SLAactivity message

* chore: move SLA spec to enterprise folder

* chore: move team activity methods to a separate module

* chore: fix typo

* chore: move sla activity message spec to conversation model

app/models/concerns/sla_activity_message_handler.rb

@@ -0,0 +1,31 @@
+module SlaActivityMessageHandler
+  extend ActiveSupport::Concern
+
+  private
+
+  def create_sla_change_activity(change_type, user_name)
+    content = case change_type
+              when 'added'
+                I18n.t('conversations.activity.sla.added', user_name: user_name, sla_name: sla_policy_name)
+              when 'removed'
+                I18n.t('conversations.activity.sla.removed', user_name: user_name, sla_name: sla_policy_name)
+              when 'updated'
+                I18n.t('conversations.activity.sla.updated', user_name: user_name, sla_name: sla_policy_name)
+              end
+    ::Conversations::ActivityMessageJob.perform_later(self, activity_message_params(content)) if content
+  end
+
+  def sla_policy_name
+    SlaPolicy.find_by(id: sla_policy_id)&.name || ''
+  end
+
+  def determine_sla_change_type
+    sla_policy_id_before, sla_policy_id_after = previous_changes[:sla_policy_id]
+
+    if sla_policy_id_before.nil? && sla_policy_id_after.present?
+      'added'
+    elsif sla_policy_id_before.present? && sla_policy_id_after.nil?
+      'removed'
+    end
+  end
+end