feat(acl): store a diploma in the Documenten API and relate it to the zaak (refs #103)

IZaakGateway.StoreDocumentAsync creates an enkelvoudiginformatieobject (base64
inhoud, buffered non-chunked body, no CRS) and relates it via zaakinformatieobjecten;
AclService.StoreDiplomaAsync default-fills the ZGW document fields (informatieobjecttype,
bronorganisatie, taal nld, creatiedatum); POST /documenten exposes it. Adds the
InformatieobjecttypeUrl default (wired in a following infra commit).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

services/acl/Acl.Application/AclDefaults.cs

@@ -7,4 +7,8 @@ public sealed class AclDefaults
     public required string VerantwoordelijkeOrganisatie { get; init; }
     public required string Vertrouwelijkheidaanduiding { get; init; }
     public required Uri ZaaktypeUrl { get; init; }
+
+    /// <summary>The informatieobjecttype an uploaded diploma is filed under (S-10b). Seeded in the
+    /// catalogus and injected like <see cref="ZaaktypeUrl"/>.</summary>
+    public required Uri InformatieobjecttypeUrl { get; init; }
 }