[7.17](backport #37229) Only log events at debug level (#37256)

The Elasticsearch client was logging raw events in error and warn level, this commit makes it only log the raw events (or any event data) at debug level. This means the error message returned by Elasticsearch is now only available at debug level because it can contain the whole value of a field causing a mapping conflict.

---------

Co-authored-by: Craig MacKenzie <[email protected]>
(cherry picked from commit ac7309a)

CHANGELOG.next.asciidoc

@@ -10,6 +10,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 
 *Affecting all Beats*
 
+- Avoid logging fields values when handling Elasticsearch output errors except at the debug log level. The debug log level must now be used to see detailed errors, for example mapping errors and their cause. {pull}37229[37229]
 
 *Auditbeat*
 

libbeat/outputs/elasticsearch/client.go

@@ -393,10 +393,12 @@ func (client *Client) bulkCollectPublishFails(result eslegclient.BulkResult, dat
 				result, _ := data[i].Content.Meta.HasKey(dead_letter_marker_field)
 				if result {
 					stats.nonIndexable++
-					client.log.Errorf("Can't deliver to dead letter index event %#v (status=%v): %s", data[i], status, msg)
+					client.log.Errorf("Can't deliver to dead letter index event (status=%v). Enable debug logs to view the event and cause.", status)
+					client.log.Debugf("Can't deliver to dead letter index event %#v (status=%v): %s", data[i], status, msg)
 					// poison pill - this will clog the pipeline if the underlying failure is non transient.
 				} else if client.NonIndexableAction == dead_letter_index {
-					client.log.Warnf("Cannot index event %#v (status=%v): %s, trying dead letter index", data[i], status, msg)
+					client.log.Warnf("Cannot index event (status=%v), trying dead letter index. Enable debug logs to view the event and cause.", status)
+					client.log.Debugf("Cannot index event %#v (status=%v): %s, trying dead letter index", data[i], status, msg)
 					if data[i].Content.Meta == nil {
 						data[i].Content.Meta = common.MapStr{
 							dead_letter_marker_field: true,
@@ -411,7 +413,8 @@ func (client *Client) bulkCollectPublishFails(result eslegclient.BulkResult, dat
 					}
 				} else { // drop
 					stats.nonIndexable++
-					client.log.Warnf("Cannot index event %#v (status=%v): %s, dropping event!", data[i], status, msg)
+					client.log.Warnf("Cannot index event (status=%v): dropping event!", status)
+					client.log.Debugf("Cannot index event %#v (status=%v): %s, dropping event! Enable debug logs to view the event and cause.", data[i], status, msg)
 					continue
 				}
 			}