Multiline parsing for fluentd

1. Proposed title of this feature request

Add multiline parsing for fluentd.
2. What is the nature and description of the request?

Customer is shipping Java logs to internal Elasticsearch. Which are splitting into multiple logs. Due to the nature of the logs they can't be combined with the detectMultilineErrors:  field as it's not an error or exception. The customer is hoping that something similar to this can be implemented

https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/multiline-parsing

3. Why does the customer need this? (List the business requirements here)

Customer needs each log  entry to ship as one full log in Kibana for ease of access and to prevent confusion.

4. List any affected packages or components.

Cluster Logging

Fluentd