chore: Enhance contact merge action for identified users (#4886)

- Discard conflicting keys 
- Do not merge if there is already an identified contact

Co-authored-by: Pranav Raj S <pranav@chatwoot.com>

app/javascript/widget/helpers/axios.js

@@ -6,7 +6,7 @@ export const API = axios.create({
   withCredentials: false,
 });
 
-export const setHeader = (key, value) => {
+export const setHeader = (value, key = 'X-Auth-Token') => {
   API.defaults.headers.common[key] = value;
 };