Remap support for the `swimlanes` transform (routing)

The swimlanes transform for Vector enables you to route events into multiple named channels, or lanes, based on supplied conditions. This can be useful for use cases like sending a subset of events to one sink and a different subset to another.

Previously, the swimlanes transform required you to specify conditions using check_fields. But now you can use Vector Remap Language expressions in the remap transform to specify those conditions. This should make using swimlanes more natural and expressive.

Example

The example configuration below shows the same swimlanes transform using the old system (check_fields) and the new system (remap):

 [transforms.split_events]
 type = "swimlanes"
 inputs = ["http-server-logs"]

 # Using check_fields
-lanes.success.type = "check_fields"
-lanes.success.status_code.eq = 200
-lanes.success.severity.eq = "info"

 # Using remap
+lanes.success.type = "remap"
+lanes.success.source = '.status_code == 200 && .severity == "info"'