This is modeled after the internal/docker package to make it easy to use as a
replacement. Instead of creating a new docker container for each test,
it will create a new database in an existing database container, using a
template database as a source. This assumes that the template database
exists and already has the schema migrations run against it.
The default template is `boundary_template` which should already have
all migrations applied. However, some tests require an empty database to
test the migration code. In these cases the `template1` template
database should be used, ie:
dbtest.StartWithTemplate("postgres", dbtest.WithTemplate("template1"))
