feat: Conversation update API for sla_policy_id (#8973)

- Add an endpoint for updating conversation attributes (priority / sla_policy_id )
- Swagger spec
- minor chores around the conversation API/spec

Fixes: https://linear.app/chatwoot/issue/CW-2100/feat-backend-api-to-update-the-sla-of-a-conversation

enterprise/app/models/applied_sla.rb

@@ -23,6 +23,13 @@ class AppliedSla < ApplicationRecord
   belongs_to :conversation
 
   validates :account_id, uniqueness: { scope: %i[sla_policy_id conversation_id] }
+  before_validation :ensure_account_id
 
   enum sla_status: { active: 0, hit: 1, missed: 2 }
+
+  private
+
+  def ensure_account_id
+    self.account_id ||= sla_policy&.account_id
+  end
 end