[firestore-bigquery-export] Disable changelog table

### [READ] Step 1: Are you in the right place?

Issues filed here should be about a feature request for a **specific extension in this repository**. To file a feature request that affects multiple extensions or the Firebase Extensions platform, please reach out to
[Firebase support](https://firebase.google.com/support/troubleshooter/report/features/) directly.

### [REQUIRED] Step 2: Extension name

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

### What feature would you like to see?

I'd like there to be an option to remove the changelog table in BigQuery as I'm only interested in current state of Firestore being visible in BigQuery, and my changelog would fill up fast and use a lot of space in BigQuery.

### How would you use it?

Would use it to disable changelog dataset, as I'm only interested in the current content.