Add Policy DSL Validator, Schema Exporter, and Simulation Smoke tools

- Implemented PolicyDslValidator with command-line options for strict mode and JSON output.
- Created PolicySchemaExporter to generate JSON schemas for policy-related models.
- Developed PolicySimulationSmoke tool to validate policy simulations against expected outcomes.
- Added project files and necessary dependencies for each tool.
- Ensured proper error handling and usage instructions across tools.

src/StellaOps.Scheduler.WebService.Tests/GlobalUsings.cs

@@ -0,0 +1,6 @@
+global using System.Net.Http.Json;
+global using System.Text.Json;
+global using System.Text.Json.Serialization;
+global using System.Threading.Tasks;
+global using Microsoft.AspNetCore.Mvc.Testing;
+global using Xunit;