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/Defaults/DbServiceHealthCheck.cs

@@ -0,0 +1,21 @@
+namespace HrynCo.Common.HealthChecks.Defaults;
+
+using HrynCo.Common.HealthChecks.Interfaces;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+public sealed class DbServiceHealthCheck : IServiceHealthCheck
+{
+    private readonly IDatabaseConnectionChecker _checker;
+
+    public DbServiceHealthCheck(IDatabaseConnectionChecker checker)
+    {
+        _checker = checker;
+    }
+
+    public async Task<HealthCheckResult> CheckHealthAsync(CancellationToken cancellationToken)
+    {
+        return await _checker.CanConnectAsync(cancellationToken)
+            ? HealthCheckResult.Healthy("Database reachable")
+            : HealthCheckResult.Unhealthy("Database unreachable");
+    }
+}