feat: add sla events table (#9126)

* feat: add sla events table

* chore: refactor to EE namespace

* chore: refactor

* chore: fix spec

* chore: add references to account,inbox,sla_policy

* chore: update specs

* chore: update spec to check backfilling id's

* Update spec/enterprise/models/sla_event_spec.rb

db/migrate/20240319062553_create_sla_events.rb

@@ -0,0 +1,16 @@
+class CreateSlaEvents < ActiveRecord::Migration[7.0]
+  def change
+    create_table :sla_events do |t|
+      t.references :applied_sla, null: false
+      t.references :conversation, null: false
+      t.references :account, null: false
+      t.references :sla_policy, null: false
+      t.references :inbox, null: false
+
+      t.integer :event_type
+      t.jsonb :meta, default: {}
+
+      t.timestamps
+    end
+  end
+end