Support for atomic transactions across postgres & duckdb

[SebastienGllmt]

As mentioned in the docs, 2PC (two-phase commit) is not currently supported. Since two phased commit is a feature that has been talked about as something that may be added in the future (although difficult to implement), I wanted to create a discussion for this so that:

1. People can subscribe to this discussion to get updates if/when this feature gets implemented
2. If you search in this repo for specific terms, you will find this discussion (instead of no results)

related terms: atomic, XA, prepare, commit, atomic, transaction, saga, coordinator, eventual consistency, ACID