Message_templates.FilterFilter predicates for log events
type t = Log_event.t -> boolFilter function type
val property_filter : string -> (Yojson.Safe.t -> bool) -> tFilter by property value - event must have the property and pass the predicate
val matching : string -> tFilter that matches if a property name exists (regardless of value)
val always_pass : tAlways include filter - passes everything
val always_block : tAlways exclude filter - blocks everything