Add a filter API to plugins to decide whether to track an event or not (close #608)

[matus-tomlein]

Issue #608

Adds a new filter callback to plugins which enables deciding whether to track an event or not. This can be useful for filtering auto-tracked events by the tracker.

For instance, this snippet filters screen view events to keep only ones with a specific name property:

plugin.filter(
    schemas = listOf(
        "iglu:com.snowplowanalytics.snowplow/screen_view/jsonschema/1-0-0", // screen view events
    )
) { event ->
    event.payload["name"] == "Home Screen"
}

Documentation

Here is a commit adding the documentation for the filter function.

[mscwilson]

LGTM