logging_to_files

There sould be an option to make filebeat write it's logs to file.
Like the logging_to_syslog configuration it's possible to add logging_to_files configuration (https://www.elastic.co/guide/en/beats/filebeat/current/configuration-logging.html#_literal_logging_to_files_literal).
It's also possible to add configuration for the log directory and name (logging.files.path and logging.files.name).

Start by finding the existing logging_to_syslog configuration and compare it with the Filebeat logging configuration documentation linked in the issue. Add equivalent file logging support, including logging.files.path and logging.files.name, and verify that the charm exposes these options as configuration.

Written by the indexing model from the issue text.