[Stack Monitoring] Create simulator for stack monitoring data

[matschaffer]

In order to test new kibana metrics formats (#113149) ahead of metricbeat being available (elastic/beats#27569) we'll need a way to generate fake data.

It'd be great to have this in general for things like testing pagination updates, mixed version scenarios, or even answering SDHs that involve tricky data collection models (mixed mode, via logstash or not, etc).

[elasticmachine]

Pinging @elastic/infra-monitoring-ui (Team:Infra Monitoring UI)

[matschaffer]

@jasonrhodes let me know if this approach makes sense to to you. I could alternatively put this on ice until the beats work is done, then use a real stack to do dev UI work.

[matschaffer]

Just wanted to note I also tried out some other data generator tooling:

1. essiem - this has an esexport function I thought might be useful for exporting real data, but the randomization seemed very fixed on replacing only agent host name information
2. https://github.com/elastic/kibana/tree/main/packages/elastic-apm-synthtrace - this might work, but seemed to have some baked in assumptions around apm data streams. Will chat with @dgieselaar to see if he thinks it'd fit to try to have synthtrace also produce non-data-stream feeds that SM uses today.

[matschaffer]

I'm trying out #118302 for data simulation next

[matschaffer]

This is no longer a blocker for 8.0 since I was able to get the data I needed by enabling kibana's internal collection.

[matschaffer]

Moving to in progress since at least me an @miltonhultgren have been looking into it