Add a clean way to use an existing BlobContainerClient

[karl-sjogren]

I've been trying to setup Umbraco using .NET Aspire which sets up a BlobContainerClient with some extra telemetry attached. After looking at this for quite some time I managed to find a way to use that client with Umbraco like this.

public class PostConfigureAzureBlobFileSystemOptions : IPostConfigureOptions<AzureBlobFileSystemOptions> {
    private readonly BlobContainerClient _blobContainerClient;

    public PostConfigureAzureBlobFileSystemOptions(BlobContainerClient blobContainerClient) {
        _blobContainerClient = blobContainerClient;
    }

    public void PostConfigure(string? name, AzureBlobFileSystemOptions options) {
        ArgumentNullException.ThrowIfNull(options);

        options.ConnectionString = "https://not.a.real.storage.account.blob.core.windows.net/";
        options.TryCreateBlobContainerClientUsingUri(_ => _blobContainerClient);
    }
}

This does however look super hacky since I need to set the ConnectionString property to a "valid" url for the TryCreateBlobContainerClientUsingUri callback to be called :)

I'm not sure how to do this in the cleanest way though. I would love if there was some way to just take the BlobContainerClient directly from DI if available, maybe through another extension method on IUmbracoBuilder or just a settable option on AzureBlobFileSystemOptions?

At least adding a TryCreateBlobContainerClient method would be helpful so I can remove my ugly ConnectionString :)

I would be willing to contribute a PR for this, either for a simple new extension method or something even more helpful to get the BlobContainer from DI.