chore: add hrynco common library solution

- add the standalone HrynCo.Common solution and projects
- include the shared common library source and tests
- add package metadata and a repo gitignore

HrynCo.Common/HealthChecks/Interfaces/IServiceHealthCheck.cs

@@ -0,0 +1,8 @@
+namespace HrynCo.Common.HealthChecks.Interfaces;
+
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+public interface IServiceHealthCheck
+{
+    Task<HealthCheckResult> CheckHealthAsync(CancellationToken cancellationToken);
+}