Better user/role/database/etc. seeding options

[Aaron Gershman]

see:

• https://github.com/cloudfoundry-incubator/pxc-release/blob/master/jobs/pxc-mysql/templates/db_init.erb

In order to better manage how users, roles, databases, extensions, superuser service accounts, etc., all get seeded in the respective environments of ysql, yedis, and ycql, different options for initial configuration management should be considered.

E.g., maybe better .sql/.cql init scripts? a tiny go/spring boot app which can handle seeding a bit better? etc.

This also presumes a better or unified configuration declaration schema beyond the {ysql,ycql}.databases.superusers config in the deployment manifest.