fix(bigquery-connection): Fix chain authen logic when we try to create bigquery client

[lethanhduong]

Issue - context: When we deploy vanna app on a instance (Pod of K8S - GKE) which already have a default credential of a service account. However, we would like to use the other credential as input file name for the app. We cannot do it with the current logic. The lib always use default credential first.

What is the change: Changed the chain authentication logic.