Document disclosure via bulk-index error logging

Sensitive-data logging in Elastic APM Server before 8.14.0 allows remote authenticated users to expose document bodies via failed indexing requests. When Elasticsearch returns a partially failed bulk-index response such as unavailable_shards_exception, its response line contains the original document body and APM Server writes that entire line to its error log. Exploitation requires low-privileged adjacent-network access and a partial indexing failure; the bounded consequence is disclosure of document contents to parties who can read APM Server logs.