Design scale unit configuration schema

**Summary**: Define the YAML schema structure for specifying scale units in azure.yaml, including region associations, layer assignments, and parameter customization per scale unit.

**Acceptance Criteria**:
- [ ] YAML schema for scale unit definition with name and region properties
- [ ] Support for layer assignment to scale units
- [ ] Parameter override capability per scale unit
- [ ] Global vs regional layer designation
- [ ] Scale unit dependency and deployment order specification
- [ ] JSON schema definition with validation rules