Support API version 2026-04-01

The [currently supported versions](https://github.com/Azure/AppConfiguration-Emulator/blob/main/src/Azure.AppConfiguration.Emulator.Versioning/ApiVersions.cs) of App Configuration Emulator don't include [version 2026-04-01](https://learn.microsoft.com/en-us/rest/api/data-plane/appconfiguration/operation-groups?view=rest-data-plane-appconfiguration-2026-04-01&source=docs) of the Data plane API yet. Can the emulator be updated to support this new version?

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Based on the published REST API references and the Azure REST API specifications repository, the 2026-04-01 data-plane version appears to be an evolutionary update over 2024-09-01, with the most notable addition being explicit support for tracking long-running operations (LROs) for snapshot-related operations.

Summary of the changes generated with Copilot:

| Area | 2024-09-01 | 2026-04-01 | Difference |
|--------|--------|--------|--------|
| Long-running operation status endpoint | No dedicated `GET /operations` endpoint is documented in this version. Snapshot creation returns an `Operation-Location` header. | New `GET /operations?snapshot={name}` endpoint returns operation state (`Running`, etc.), operation ID, error details, and retry information. | **New capability:** clients can explicitly poll operation status rather than relying solely on response headers. |
| Snapshot operation model | Snapshot creation supports asynchronous behavior via the `Operation-Location` response header. | Snapshot operations are integrated with a documented long-running operation (LRO) pattern that includes a dedicated status resource. | **More complete LRO support** and a clearer REST contract for asynchronous snapshot processing. |
| Operation status schema | Not documented as a public resource. | Introduces an `Operation Details` resource containing `id`, `status`, and structured error information. | **New resource type** exposed by the API. |
| Error model | Uses App Configuration error objects. | Adds Azure Core-style error definitions for operation tracking responses (`Error`, `InnerError`, detailed error hierarchy). | **Expanded error contract** for operation-status APIs. |
| Overall resource set | Includes keys, key-values, labels, revisions, locks, and snapshot APIs. | Retains existing resource areas and adds documented operation-tracking APIs. | No major resource removals observed; API surface is extended rather than replaced. |

Start with src/Azure.AppConfiguration.Emulator.Versioning/ApiVersions.cs and compare the existing 2024-09-01 support with the published 2026-04-01 REST references and Azure REST API specifications. Trace the emulator's snapshot handling to determine the required operation-status behavior; done means the new API version and its documented snapshot LRO surface are supported.

Written by the indexing model from the issue text.