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/controllers/enterprise/api/v1/accounts/conversations_controller.rb

@@ -0,0 +1,5 @@
+module Enterprise::Api::V1::Accounts::ConversationsController
+  def permitted_update_params
+    super.merge(params.permit(:sla_policy_id))
+  end
+end