feat: sla 1 - refactor sla_policies model and add applied_sla model (#8602)

* feat: add models

* chore: refactor sla column names

* chore: remove foreign keys

* chore: fix spec

* chore: refactor models

spec/enterprise/models/applied_sla_spec.rb

@@ -0,0 +1,16 @@
+require 'rails_helper'
+
+RSpec.describe AppliedSla, type: :model do
+  describe 'associations' do
+    it { is_expected.to belong_to(:sla_policy) }
+    it { is_expected.to belong_to(:account) }
+    it { is_expected.to belong_to(:conversation) }
+  end
+
+  describe 'validates_factory' do
+    it 'creates valid applied sla policy object' do
+      applied_sla = create(:applied_sla)
+      expect(applied_sla.sla_status).to eq 'active'
+    end
+  end
+end