[stack monitoring] remove beta flags

[klacabane]

Summary

The data streams powering stack monitoring are flagged as beta in elasticsearch/kibana/logstash packages. We can remove these flags to make them ga as satisfying testing/bugfix was done

### Tasks
- [ ] https://github.com/elastic/integrations/pull/8044
- [ ] https://github.com/elastic/kibana/pull/167867
- [ ] https://github.com/elastic/kibana/issues/175794

[miltonhultgren]

@klacabane Is this still in progress?

[klacabane]

I'll merge the pending doc PR and create backlog issue for the suggested improvement

[klacabane]

Closing as core work is complete but elastic/kibana#175794 won't be prioritized for now