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

app/controllers/concerns/access_token_auth_helper.rb

@@ -1,6 +1,6 @@
 module AccessTokenAuthHelper
   BOT_ACCESSIBLE_ENDPOINTS = {
-    'api/v1/accounts/conversations' => %w[toggle_status toggle_priority create],
+    'api/v1/accounts/conversations' => %w[toggle_status toggle_priority create update],
     'api/v1/accounts/conversations/messages' => ['create'],
     'api/v1/accounts/conversations/assignments' => ['create']
   }.freeze