* docs: improve RBAC and role creation documentation
- Clarify that file-based RBAC provisioning is for self-managed instances only
- Distinguish between Grafana Admin (Server Admin) and Org Admin
- Remove incorrect UI instructions for custom role creation
- Add Terraform example for creating custom roles and assignments
* Apply suggestions from code review
Co-authored-by: Anna Urbiztondo <anna.urbiztondo@grafana.com>
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Co-authored-by: Anna Urbiztondo <anna.urbiztondo@grafana.com>