Following the work done here - elastic/beats#21965

We should now work on collecting metrics and some other tasks:

• Libbeat collects metrics every 10s into ring buffer (N=60)
• Expose internal metrics via API
• elastic-agent diagnostics: filebeat and metricbeat configuration beats#29898
• Diagnostics tool reads metrics ring buffer
• (optional) CLI subcommand diag add to add extra files and directories to a diagnostics report.
  log / capture std from the processes started
• Remove credentials being dumped as part of the diagnotic command