Investigate supporting an in memory database

[machristie]

The data catalog implementation leans heavily on PostgreSQL features, but perhaps it's possible to provide an alternate implement for something like the H2 in memory database. This would make it easier to get started with development on data catalog and could also be used for unit tests.

In general, if the in memory database supports a JSON column type, the integration should be possible. The search need not be as performant or reliant upon indexes as the PostgreSQL implementation.