Create data migration for first step of schema transition

Note that this depends on [PR 2](https://github.com/cbmi/varify-data-warehouse/pull/2).  The attached PR shall be invalid until this merge is complete.

This shall be a reversible data migration to complete the first step of the greater transition to a new schema.
Consider changing this to the following:

```python
if result.genotype.label in ['#/#', '1/1', '1/2', '2/2#']:
    ...
```