Use IHttpClientFactory to avoid socket exhaustion in DefaultRestCaller

[tusmester]

We should NOT instantiate HttpClient directly but through the factory that will handle the connection pooling for us.

For details: https://learn.microsoft.com/en-us/dotnet/architecture/microservices/implement-resilient-applications/use-httpclientfactory-to-implement-resilient-http-requests

• see the ProcessWebRequestResponsePrivateAsync method
• add the Microsoft.Extensions.Http NuGet package
• add the service using AddHttpClient()
• inject the IHttpClientFactory service to DefaultRestCaller
• use it:

using HttpClient client = _httpClientFactory.CreateClient();