Problem: Extension copy is not resumable

[arajkumar]

Attempt copying extension using pgcopydb copy extensions and interrupt the copy in the middle. When you resume extension copy again, it would attempt copying already processed extension configuration tables.

I think we can solve this by introducing a transaction to handle the extension config table copy along with sqlite summary entry to skip if transaction is already complete.

[dimitri]

Sounds familiar... #725 ?

[arajkumar]

@dimitri Yes, I will polish #725 to address this.