Fix error spam on AKS

This was happening due to the error level logging when the log path
matcher detected a `log.file.path` that does not start with a standard
Docker container log folder `/var/lib/docker/containers` because AKS
dropped support for Docker in September 2022 and switched to containerd.

It looks like this message was not supposed to be on the error level
in the first place since it just means that the matcher didn't
match and it's not an error. But it was mistakenly promoted from the
debug level in elastic#16866 most likely
because the message started with `Error` and looked confusing.

This a partial fix to unblock our customers, but we still need to come
up with the full AKS/containerd support in a follow up change.

filebeat/processor/add_kubernetes_metadata/matchers.go

@@ -92,7 +92,7 @@ func (f *LogPathMatcher) MetadataIndex(event mapstr.M) string {
 	f.logger.Debugf("Incoming log.file.path value: %s", source)
 
 	if !strings.Contains(source, f.LogsPath) {
-		f.logger.Errorf("Error extracting container id - source value does not contain matcher's logs_path '%s'.", f.LogsPath)
+		f.logger.Debugf("log.file.path value does not contain matcher's logs_path '%s', skipping...", f.LogsPath)
 		return ""
 	}