azure-libraries-for-net: [BUG] SDK creates a lot of HttpClient causing connection starvation

Describe the bug When using the SDK for long-running processes, we’ve noticed that it’s causing Linux workloads to run out of connections (https://github.com/tomkerkhove/promitor/issues/798).

After digging deeper, we thought we were not using the SDK correctly so we’ve POCed a refactoring where we only authenticate once and re-use it for the rest of the processing (https://github.com/tomkerkhove/promitor/pull/844).

After digging deeper, @maartenba found that the SDK is creating a lot of HttpClients and not re-using them.

Is this on purpose or is this a bug?

Exception or Stack Trace

System.Net.Http.HttpRequestException: Too many open files in system ---> System.Net.Sockets.SocketException: Too many open files in system
   at System.Net.Sockets.Socket..ctor(AddressFamily addressFamily, SocketType socketType, ProtocolType protocolType)
   at System.Net.Sockets.DualSocketMultipleConnectAsync..ctor(SocketType socketType, ProtocolType protocolType)
   at System.Net.Sockets.Socket.ConnectAsync(SocketType socketType, ProtocolType protocolType, SocketAsyncEventArgs e)
   at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)

To Reproduce Steps to reproduce the behavior:

• Authenticate client
• Have look how many clients are created

Expected behavior Re-use of one HttpClient rather than 70+

Setup (please complete the following information):

• OS: Linux
• IDE : Visual Studio
• Version of the Library used: 1.30.0

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