Allow to control Beats logging

Beats logging configuration is quite flexible, but currently the Elastic-Agent does not allow for a detailed configuration of it. If the logs are too verbose when running `elastic-agent diagnostics collect` the time window of the logs can be very small and the logs might be flooded with messages from selectors that are not needed.

Here is Filebeat logging configuration:
https://github.com/elastic/beats/blob/9e0ce3b26a762f0e0ac246654797624bfaab8cc9/filebeat/filebeat.reference.yml#L2478-L2546

It would be nice to be able to at least set:
* logging.selectors
* logging.files.rotateeverybytes
* logging.files.keepfiles