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/sla_policy_spec.rb

@@ -18,6 +18,11 @@ RSpec.describe SlaPolicy, type: :model do
     it 'creates valid sla policy object' do
       sla_policy = create(:sla_policy)
       expect(sla_policy.name).to eq 'sla_1'
+      expect(sla_policy.first_response_time_threshold).to eq 2000
+      expect(sla_policy.description).to eq 'SLA policy for enterprise customers'
+      expect(sla_policy.next_response_time_threshold).to eq 1000
+      expect(sla_policy.resolution_time_threshold).to eq 3000
+      expect(sla_policy.only_during_business_hours).to be false
     end
   end
 end