fix(whatsapp): allow calling a contact with no existing conversation (#15014)

## Description

Agents can now place a WhatsApp call to a contact straight from the
contacts screen, even if that contact has never messaged in. Previously
the call only worked once a conversation already existed, so a freshly
added contact would fail with "Unable to start the call. Please try
again." — the only workaround was to get the contact to message the
channel first.


## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

- Manually via UI

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/dashboard/api/channel/whatsapp/whatsappCallsAPI.js

@@ -10,10 +10,13 @@ class WhatsappCallsAPI extends ApiClient {
     return axios.get(`${this.url}/${callId}`).then(r => r.data);
   }
 
-  initiate(conversationId, sdpOffer) {
+  // Either conversationId, or contactId + inboxId to let the BE resolve the conversation.
+  initiate({ conversationId, contactId, inboxId }, sdpOffer) {
     return axios
       .post(`${this.url}/initiate`, {
         conversation_id: conversationId,
+        contact_id: contactId,
+        inbox_id: inboxId,
         sdp_offer: sdpOffer,
       })
       .then(r => r.data);