[Q2 FY27] Better document Kibana privileges and when they're required

- The privilege model in Kibana is based on per-space, per-feature "All - Read - Custom" permissions
- Sometimes these are associated with elasticsearch level privileges

The goal of this task is to review and make these consistent

Why?
We sometimes talk about "Edit" or "Write" or "Read" permissions/privileges, which is sometimes not super clear if we're referring to Kibana privileges or Elasticsearch or both. This is a meta task as we need to

- [ ] make sure the correct privileges are listed as clear requirements
- [ ] make sure these privileges are referenced to clearly and consistently with the documented user role model

This needs to be checked in:

- [ ] explore and analyze
- [ ] solutions/observability
- [ ] solutions/security
- [ ] API docs
- [ ] To assess if this needs to be extended to other areas too