Add example for installing postgres database

This example manifest deploys Postgres 9.2 which avoid the problem of starting
with an ancient version of postgres (8.4 on RHEL) that fails the database
migration task with the following error:

```
bin/razor-admin -e production migrate-database
...
Java::OrgPostgresqlUtil::PSQLException: ERROR: syntax error at or near
"DEFERRABLE"
```