chore: import Musify.WebApi into monorepo (preserving history)

git-subtree-dir: Musify.WebApi
git-subtree-mainline: 9d433868cc
git-subtree-split: ca8750c3b4

Musify.WebApi/WebApi/Filters/ValidationFilter.cs

@@ -0,0 +1,20 @@
+using FluentValidation;
+
+namespace WebApi.Filters;
+
+public sealed class ValidationFilter<T>(IValidator<T> validator) : IEndpointFilter where T : class
+{
+    public async ValueTask<object?> InvokeAsync(EndpointFilterInvocationContext context, EndpointFilterDelegate next)
+    {
+        var argument = context.Arguments.OfType<T>().FirstOrDefault();
+
+        if (argument is null)
+            return await next(context);
+
+        var result = await validator.ValidateAsync(argument, context.HttpContext.RequestAborted);
+
+        return result.IsValid
+            ? await next(context)
+            : Results.ValidationProblem(result.ToDictionary());
+    }
+}