[firestore-bigquery-export] Add collection group path template to import script

[jsnee]

[REQUIRED] Step 2: Extension name

This feature request is for extension: firestore-bigquery-export

What feature would you like to see?

I'd like to see the import script have an option to provide a path template parameter so that the importer could populate path-params

How would you use it?

This would be used to populate the path-params of imported records that are part of a collection group import as they currently do get imported without a value. If implemented, the path-params could be utilized in queries regardless of if the record was imported by the script or exported by the extension.