Configure filter type with option in audit.yaml

[eperott]

Filter types are only configurable via a system property.

We should make this configurable via the https://github.com/Ericsson/ecaudit/blob/master/conf/audit.yaml file instead.

• Configure filter type in audit.yaml
• Remain backward compatible with current setting via system property
• Configuration in audit.yaml should take precedance
• Update documentation and upgrade guide to reflect changes