Updating QS to reflect service account correct roles (#4580)

## What are you changing in this pull request and why?

Responding to feedback from customer in [ProductBoard
feedback](https://dbt-labs.productboard.com/all-notes/notes/35861924)
and verified with our [dbt Cloud and BigQuery for
Admins](https://courses.getdbt.com/courses/dbt-cloud-and-bigquery-for-admins)
course

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Adding new pages (delete if not applicable):
- [ ] Add page to `website/sidebars.js`
- [ ] Provide a unique filename for the new page

Removing or renaming existing pages (delete if not applicable):
- [ ] Remove page from `website/sidebars.js`
- [ ] Add an entry `website/static/_redirects`
- [ ] Run link testing locally with `npm run build` to update the links
that point to the deleted page

website/docs/guides/bigquery-qs.md

@@ -78,7 +78,7 @@ In order to let dbt connect to your warehouse, you'll need to generate a keyfile
     - Click **Next** to create a new service account.
 2. Create a service account for your new project from the [Service accounts page](https://console.cloud.google.com/projectselector2/iam-admin/serviceaccounts?supportedpurview=project). For more information, refer to [Create a service account](https://developers.google.com/workspace/guides/create-credentials#create_a_service_account) in the Google Cloud docs. As an example for this guide, you can:
     - Type `dbt-user` as the **Service account name**
-    - From the **Select a role** dropdown, choose **BigQuery Admin** and click **Continue** 
+    - From the **Select a role** dropdown, choose **BigQuery Job User** and **BigQuery Data Editor** roles and click **Continue** 
     - Leave the **Grant users access to this service account** fields blank
     - Click **Done**
 3. Create a service account key for your new project from the [Service accounts page](https://console.cloud.google.com/iam-admin/serviceaccounts?walkthrough_id=iam--create-service-account-keys&start_index=1#step_index=1). For more information, refer to [Create a service account key](https://cloud.google.com/iam/docs/creating-managing-service-account-keys#creating) in the Google Cloud docs. When downloading the JSON file, make sure to use a filename you can easily remember. For example, `dbt-user-creds.json`. For security reasons, dbt Labs recommends that you protect this JSON file like you would your identity credentials; for example, don't check the JSON file into your version control software.