Allow remote connections for pg_basebackup

[chrira]

The file openshift-custom-postgresql.conf.template should be extended to allow remote connections for backups with the pg_basebackup tool.

Error Message:

pg_basebackup: could not connect to server: FATAL: number of requested standby connections exceeds max_wal_senders (currently 0)

With this additional configuration, the backup works:

max_wal_senders = 5
wal_level = hot_standby
archive_mode = on
archive_command = '/bin/true'

[pkubatrh]

After #208 is merged in you will be able to extend the configuration file

[pkubatrh]

This should be fixed by #208

Feel free to re-open if you run into any problems