Add composite cursors to connectors

[tmas-definitive]

In some cases, it would be extremely helpful to have the ability to set a composite cursor to keep records up to date in an incremental replication strategy connection. An example of this would be a postgres source where we have 3 (or more) columns that can be updated indicating the record has changed

• created_at
• updated_at
• deleted_at

Right now we can only set one cursor field which means if all three fields aren't aligned (ie. created_at = updated_at on create, deleted_at = updated_at on delete) which means an update to data can be missed.