Handle saving Billing Account Contacts through the billing account page (GraphQL)

Problem

Right now, we use the REST API to update the contacts in the Billing Account Settings page. This does not provide a nice experience, since the user is navigated to the account settings page afterwards.

Proposal

Update the zuora_contact_form.vue to use the GraphQL endpoint to update the contacts.

This will ensure that the user stays on the page they were on for both the Account page and the Billing Account Settings page.

Note: Ensure error dictionary entries are added for relevant mutation or model update failures