Add SQL data type macros to dg-common

[bryantrobbins]

As a user, I want to generate data values based on SQL types (e.g., VARCHAR(255), BLOB, etc.). I should be able to use these types from any DG model as a macro.

Let's add macros for data types from Oracle and Postgres.

As with all other macros, this would generate only one value per use.

This is a separate feature from #248 and #247.

[bryantrobbins]

@leeny324 also looking into this.

[bryantrobbins]

Untagging from 2.2 as this is a bit broader.

#247 does implement part of this.

[bryantrobbins]

Whatever does get implemented here needs to conform to what was done in #247.