[Kibana] Check which settings are available on Cloud

[florent-leborgne]

More settings than those actually flagged seem to be supported on Cloud. The goal of this task is to check and update the settings docs under https://www.elastic.co/docs/reference/kibana/configuration-reference

[florent-leborgne]

For example:

these kibana settings https://www.elastic.co/docs/reference/kibana/configuration-reference/banner-settings are marked as "Self Managed" only, but I set them on Elastic Cloud Hosted and they appear to work.

[shainaraskas]

related elastic/kibana#193431

[florent-leborgne]

I didn't realize there was one issue about this already, I'll close this one as a duplicate and drop the additional feedback in that other issue.