If optional `keyfile` setting isnt defined the plugin fails

[pnadolny13]

Related to slack thread https://meltano.slack.com/archives/C01TCRBBJD7/p1664397294675829.

It looks like the file bundle installs a profile that has an optional keyfile setting, if its not provided then it uses an empty string as default but that causes a No such file or directory: '' error.

This profile will be moved to https://github.com/meltano/dbt-ext/blob/feat/working-dbt-ext/files_dbt_ext/profiles/bigquery/profiles.yaml soon.

[spacecowboy]

I can comment that it is not optional. I specify big query to use service-account method which means it's required.

but this env var is not getting set with the file path used by target bigquery