Add deprecation logs fileset to Filebeat Logstash module

**Describe the enhancement:**

Today Filebeat's [Logstash module](https://www.elastic.co/docs/reference/beats/filebeat/filebeat-module-logstash) collects regular logs as well as slowlogs. However, the module won't collect [deprecation logs](https://github.com/elastic/logstash/issues/11049). It'd be useful to collect these so administrators have better visibility/awareness of deprecations.

Start with the Filebeat Logstash module and compare its existing regular-log and slowlog filesets. Trace how those filesets collect and expose logs, then add equivalent coverage for Logstash deprecation logs. Done means administrators can collect deprecation logs through the module alongside the existing log types.

Written by the indexing model from the issue text.