Add extensions for Delete/Close methods that don't throw in NotFound.

[inikulshin]

For example

async Task DeleteVhostAsync(
    string vhostName,
    bool throwOnNotFound,
    CancellationToken cancellationToken = default)
{
    try
    {
        await DeleteVhostAsync(vhostName, cancellationToken);
    }
    catch (UnexpectedHttpStatusCodeException ex) when (!throwOnNotFound && ex.StatusCode == HttpStatusCode.NotFound)
    {
    }
}

Inspired by
https://learn.microsoft.com/en-us/dotnet/api/microsoft.win32.registrykey.deletesubkey?view=net-8.0
https://learn.microsoft.com/en-us/dotnet/api/microsoft.win32.registrykey.deletevalue?view=net-8.0