fix: Fixes reply-to in WhatsApp Cloud API (#13467)

This change https://github.com/chatwoot/chatwoot/pull/13371 broke the
functionality. When a user replies to a WhatsApp message, the reply
context wasn't being properly stored in Chatwoot due to #13371

WhatsApp sends reply messages with a `context` field containing the
original message ID:
```json
{
    "messages": [{
      "context": {
        "from": "phone_number",
        "id": "wamid.ORIGINAL_MESSAGE_ID"
      },
      "from": "phone_number",
      "id": "wamid.REPLY_MESSAGE_ID",
      "text": { "body": "This is a reply" }
    }]
  }
```
However, the in_reply_to_external_id was being overridden when building
the message because content_attributes was explicitly set to either {
external_echo: true } or {}, which discarded the reply-to information.

app/services/whatsapp/incoming_message_base_service.rb

@@ -175,6 +175,9 @@ class Whatsapp::IncomingMessageBaseService
   end
 
   def create_message(message, source_id: nil)
+    content_attrs = outgoing_echo ? { external_echo: true } : {}
+    content_attrs[:in_reply_to_external_id] = @in_reply_to_external_id if @in_reply_to_external_id.present?
+
     @message = @conversation.messages.build(
       content: message_content(message),
       account_id: @inbox.account_id,
@@ -184,8 +187,7 @@ class Whatsapp::IncomingMessageBaseService
       status: outgoing_echo ? :delivered : :sent,
       sender: outgoing_echo ? nil : @contact,
       source_id: (source_id || message[:id]).to_s,
-      content_attributes: outgoing_echo ? { external_echo: true } : {},
-      in_reply_to_external_id: @in_reply_to_external_id
+      content_attributes: content_attrs
     )
   end