core: fix schema public with PostgreSQL 15

[bruno-at-bareos]

In PostgreSQL 15 create/modify right were removed from public schema, making all temp tables creation failing.

• This PR enables again the create right for the bareos database user.
• For Debian dbconfig we now use the reassign owned instruction so view and function are also handled correctly.
• ReadOnly user template is also renewed with schema.

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[pstorz]

Good work!