feat: config & schema expansion for all load test profiles

[kristopherjturner]

Overview

Expand the configuration schema and YAML variable system to fully support all planned load testing profiles (FIO, HammerDB, iPerf, stress-ng, VMFleet). The configuration layer must be the single source of parameters for all test workloads.

Scope

• Extend config/variables.example.yml with all test profile parameters
• Define JSON Schema for all profile-level config files under config/schema/
• Add per-tool config templates (FIO job files, HammerDB scripts, iPerf arguments)
• Validate config against schema as part of the test invocation flow
• Document all configuration parameters in the docs site

Acceptance Criteria

• All tool-specific parameters are definable in YAML config (no hard-coded values)
• JSON Schema validation runs on startup and fails fast on invalid config
• Example config provided for each supported tool
• Schema documented in docs/configuration/

Dependencies

• Parent Epic: [Epic] Load Testing Toolkit Full Build-Out #8
• Toolkit variable registry: Create master variables registry to standardize variables across all repos azurelocal-toolkit#4