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/BaseConfigurationCheck.cs

@@ -0,0 +1,39 @@
+namespace HrynCo.Common.HealthChecks;
+
+using System.ComponentModel.DataAnnotations;
+using HrynCo.Common.HealthChecks.Interfaces;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+public abstract class BaseConfigurationCheck<TOptions> : IConfigurationCheck
+    where TOptions : class
+{
+    private readonly string _name;
+    private readonly TOptions _options;
+
+    protected BaseConfigurationCheck(TOptions options, string name)
+    {
+        _options = options;
+        _name = name;
+    }
+
+    public Task<HealthCheckResult> CheckConfigurationAsync(CancellationToken cancellationToken)
+    {
+        var context = new ValidationContext(_options);
+        var results = new List<ValidationResult>();
+
+        bool isValid = Validator.TryValidateObject(
+            _options,
+            context,
+            results,
+            true
+        );
+
+        if (!isValid)
+        {
+            string errors = string.Join("; ", results.Select(r => r.ErrorMessage));
+            return Task.FromResult(HealthCheckResult.Unhealthy($"{_name} configuration invalid: {errors}"));
+        }
+
+        return Task.FromResult(HealthCheckResult.Healthy($"{_name} configuration is valid."));
+    }
+}