Upgrade Zendesk integration for multi-brand

Currently the integration does not correctly manage Zendesk instances which are multi-brand.
For exemple, our Zendesk instance is organized with multiple brands:
- 4 brands for supporting our clients
- 2 brands for supporting certain end-users
- 4 or 5 additional brands for [mention specific purpose]zendesk

Our community is primarily aimed at our clients, so we want to ensure that:

1. Federated search: We want the federated search to include content from the Zendesk Guide of our 4 client support brands. Currently, the search only covers the default brand in Zendesk. As it stands, the federated search is incomplete.

2. Self-service score calculation: Currently, the self-service score calculation aggregates tickets from all Zendesk brands, whereas we only want to consider tickets from our 4 client support brands. This results in inaccurate calculations that cannot be effectively utilized.