RMB-1052: ERROR: 42501: permission denied for "CREATE SCHEMA IF NOT EXISTS"

https://folio-org.atlassian.net/browse/RMB-1052

As a sysop I need to remove the CREATE privilege for the database from the postgres role an RMB based module uses (principle of least privileges).

The CREATE privilege for the database is not needed after the tenant-module schema has been created.

However, when upgrading a tenant to a new module version RMB executes `CREATE SCHEMA IF NOT EXISTS` that fails if the privilege has been removed,
even if the schema exists:

```
ERROR:  42501: permission denied for database postgres
```

Fix: Skip that `CREATE SCHEMA` statement if the schema already exists.

Author: julianladisch

domain-models-runtime/src/main/resources/templates/db_scripts/create.ftl

@@ -12,7 +12,14 @@ BEGIN
   GRANT ${myuniversity}_${mymodule} TO CURRENT_USER;
 END $$;
 
-CREATE SCHEMA IF NOT EXISTS ${myuniversity}_${mymodule} AUTHORIZATION ${myuniversity}_${mymodule};
+DO $$
+BEGIN
+  PERFORM FROM information_schema.schemata WHERE schema_name = '${myuniversity}_${mymodule}';
+  IF FOUND THEN
+    RETURN;
+  END IF;
+  CREATE SCHEMA IF NOT EXISTS ${myuniversity}_${mymodule} AUTHORIZATION ${myuniversity}_${mymodule};
+END $$;
 
 </#if>