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

db/migrate/20231223033019_refactor_sla_policy_columns.rb

@@ -0,0 +1,8 @@
+class RefactorSlaPolicyColumns < ActiveRecord::Migration[7.0]
+  def change
+    rename_column :sla_policies, :rt_threshold, :next_response_time_threshold
+    rename_column :sla_policies, :frt_threshold, :first_response_time_threshold
+    add_column :sla_policies, :description, :string
+    add_column :sla_policies, :resolution_time_threshold, :float
+  end
+end

db/migrate/20231223040257_create_applied_slas.rb

@@ -0,0 +1,13 @@
+class CreateAppliedSlas < ActiveRecord::Migration[7.0]
+  def change
+    create_table :applied_slas do |t|
+      t.references :account, null: false
+      t.references :sla_policy, null: false
+      t.references :conversation, null: false
+
+      t.string :sla_status
+
+      t.timestamps
+    end
+  end
+end