[Monitoring] Aligning Stack Monitoring with the Kibana/Spaces security model

[chrisronline]

Per our goal to remove internal collection in 8.0, I think we can more closely align with the Kibana/Spaces security model. Historically, we required a reserved role for accessing the Stack Monitoring UI, but the writes that required that reserved role will go away with internal collection.

We should investigate/open a PR removing this reserved role requirement and define the necessary privileges within the Kibana/Spaces security model.

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)

[smith]

Not prioritizing this at this time.