When using the admin -> Customer Address API , the system allows creating multiple default addresses for the same customer.

[harshit-webkul]

Describe the bug
When using the admin -> Customer Address API , the system allows creating multiple default addresses for the same customer.

To Reproduce
Steps to reproduce the behavior:

1. Use the admin -> Create Address API to add a customer address with "defaultAddress: true"
2. Create another address using the same API request and again set "defaultAddress: true"
3. Check the database and shop front.

Expected behavior
Only one default address should exist for each customer.

Screenshots
If applicable, add screenshots to help explain your problem.

Actual Result:

The API allows multiple default addresses for the same customer.
Existing default addresses are not updated or unset.