Defer SQL initialization to fit with JPA better

Added 2 new spring.datasource.* properties ("data" like
"schema", and "deferDdl" like the "spring.jpa.hibernate.*"
flag). The SQL scripts are then run separately and the "data"
ones are triggered by a new DataSourceInitializedEvent,
which is also published by the Hibernate DDL schema export.

Fixes gh-1006