Feature Request: Support Managed Service Identity for Service Bus

[Zenuka]

Simmilar to the feature request done by NullMDR (#2109) but for service bus.
It would be nice to have build in support for managed service identity & azure service bus.

Known workarounds

I've made a workaround based on NullMDR's workaround for using MSI & storage.
Create the following class:

// Source: https://github.com/Azure/azure-webjobs-sdk/blob/dev/src/Microsoft.Azure.WebJobs.Extensions.ServiceBus/MessagingProvider.cs
public class ManagedIdentityMessagingProvider : MessagingProvider
{
    private readonly ServiceBusOptions _options;
    private readonly ConcurrentDictionary<string, MessageReceiver> _messageReceiverCache = new ConcurrentDictionary<string, MessageReceiver>();
    private readonly ConcurrentDictionary<string, MessageSender> _messageSenderCache = new ConcurrentDictionary<string, MessageSender>();

    public ManagedIdentityMessagingProvider(IOptions<ServiceBusOptions> serviceBusOptions) : base(serviceBusOptions)
    {
        _options = serviceBusOptions?.Value ?? throw new ArgumentNullException(nameof(serviceBusOptions));
    }

    public override MessageProcessor CreateMessageProcessor(string entityPath, string connectionString)
    {
        return new MessageProcessor(CreateMessageReceiver(entityPath, connectionString), _options.MessageHandlerOptions);
    }

    public override MessageReceiver CreateMessageReceiver(string entityPath, string connectionString)
    {
        return GetOrAddMessageReceiver(entityPath, connectionString);
    }

    public override MessageSender CreateMessageSender(string entityPath, string connectionString)
    {
        return GetOrAddMessageSender(entityPath, connectionString);
    }

    private MessageReceiver GetOrAddMessageReceiver(string entityPath, string connectionString)
    {
        string cacheKey = $"{entityPath}-{connectionString}";
        return _messageReceiverCache.GetOrAdd(cacheKey,
            new MessageReceiver(connectionString, entityPath, TokenProvider.CreateManagedServiceIdentityTokenProvider())
            {
                PrefetchCount = _options.PrefetchCount
            });
    }

    private MessageSender GetOrAddMessageSender(string entityPath, string connectionString)
    {
        string cacheKey = $"{entityPath}-{connectionString}";
        return _messageSenderCache.GetOrAdd(cacheKey, new MessageSender(connectionString, entityPath, TokenProvider.CreateManagedServiceIdentityTokenProvider()));
    }
}

Register it like this:

var builder = new HostBuilder()
    .ConfigureWebJobs(b => 
    {
        b.Services.AddSingleton<MessagingProvider, ManagedIdentityMessagingProvider>();
        b.AddServiceBus();
    })