Move BigQuery integration to use service accounts

[onejgordon]

GCP has updated their policy which now prevents Flow's current technique for syncing user data to their configured BigQuery table.

Suggestions from Google:

We recommend using service accounts for this type of information exchange. You can access data from your users’ Google Cloud Platform project by asking them to create a service account and update their Cloud IAM Policies in order to grant your project appropriate access. Please take a look at the articles below in order to familiarize yourself and educate your users on using service account and updating the Cloud IAM policies.

Service Account Creation:
Using OAuth 2.0 for Server to Server Applications
Service Accounts
IAM Policy:
IAM Policies
IAM Quickstart
If any of your users are having issues creating a service account or granting your project the appropriate permissions via the IAM Policies, please direct them to Google Cloud Support.