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

enterprise/app/models/applied_sla.rb

@@ -0,0 +1,23 @@
+# == Schema Information
+#
+# Table name: applied_slas
+#
+#  id              :bigint           not null, primary key
+#  sla_status      :string
+#  created_at      :datetime         not null
+#  updated_at      :datetime         not null
+#  account_id      :bigint           not null
+#  conversation_id :bigint           not null
+#  sla_policy_id   :bigint           not null
+#
+# Indexes
+#
+#  index_applied_slas_on_account_id       (account_id)
+#  index_applied_slas_on_conversation_id  (conversation_id)
+#  index_applied_slas_on_sla_policy_id    (sla_policy_id)
+#
+class AppliedSla < ApplicationRecord
+  belongs_to :account
+  belongs_to :sla_policy
+  belongs_to :conversation
+end