feat: outbound voice call essentials (#12782)

- Enables outbound voice calls in voice channel . We are only caring
about wiring the logic to trigger outgoing calls to the call button
introduced in previous PRs. We will connect it to call component in
subsequent PRs

ref: #11602 

## Screens

<img width="2304" height="1202" alt="image"
src="https://github.com/user-attachments/assets/b91543a8-8d4e-4229-bd80-9727b42c7b0f"
/>

<img width="2304" height="1200" alt="image"
src="https://github.com/user-attachments/assets/1a1dad2a-8cb2-4aa2-9702-c062416556a7"
/>

---------

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Vishnu Narayanan <vishnu@chatwoot.com>

app/javascript/dashboard/api/contacts.js

@@ -47,6 +47,12 @@ class ContactAPI extends ApiClient {
     return axios.get(`${this.url}/${contactId}/labels`);
   }
 
+  initiateCall(contactId, inboxId) {
+    return axios.post(`${this.url}/${contactId}/call`, {
+      inbox_id: inboxId,
+    });
+  }
+
   updateContactLabels(contactId, labels) {
     return axios.post(`${this.url}/${contactId}/labels`, { labels });
   }