…pportunity (#1794)

## Summary
Fixes #1745

### Time to review: __10 mins__

## Changes proposed
Setup the transformation process script structure

Implement some shared utilities that subsequent PRs will use

Implement the transformation logic for opportunities

## Context for reviewers
A lot of setup in this PR, a lot that can be reused in the subsequent
PRs to add transformations for the other sets of tables. Tried to make
sure those would require refactoring or pulling out implementation
details by setting up utils like the timestamp conversions + initial
query to the DB to fetch the transforming records.

As far as the implementation goes, determining what needs to be
transformed is pretty simple - the `transformed_at` column is null.
There is then a second column that says whether the record should be
deleted or not. When we query the staging tables, we also join with the
relevant table we'll transform to (opportunity in this case), that way
we already have the "source" and "destination" records and just need to
modify the destination record (or create it if its an insert).