Made HttpClient static and reordered requests to assume happy path first.

Results from this MR:

	100 Requests	200 Requests	500 Requests	3 Requests*
CurrentAvg	259 ms	258 ms	267 ms	432 ms
NewAvg	40 ms	43 ms	Exception**	192 ms
Improvement %	84.56%	83.33%	?	55.56%

*The 3 requests is the most realistic scenario. And this also includes the HttpPackageRepository instantiation and not only checking the version as the hundreds of requests, which is fairer, as the HttpClient is moved to be instantiated statically. ** Using this new implementation, I was simply not able to check 500 times as fast as possible towards http://packages.opentap.io due to a WebException where the repo was not answering. I'm guessing that this is due to too much load on the webserver with 500 requests:

• HttpReponse http://packages.opentap.io = {"Response status code does not indicate success: 400 (Bad Request)."}
• HttpResponse http://packages.opentap.keysight.com = Response status code does not indicate success: 500 (Internal Server Error).

TestMethod used to test this (adjust times and move stopwatch.Restart(); for different tests):

        [Test]
        public void TestVersion()
        {
            List<long> timings = new List<long>();
            int times = 500;
            Stopwatch stopwatch = Stopwatch.StartNew();
            for (int i = 0; i < times; i++)
            {
                var type = PackageRepositoryHelpers.DetermineRepositoryType("http://packages.opentap.io");
                if (type is HttpPackageRepository packageRepository)
                {
                    stopwatch.Restart();
                    Console.WriteLine(packageRepository.Version);
                    var time = stopwatch.ElapsedMilliseconds;
                    timings.Add(time);
                }

            }
            Console.WriteLine($"Average: {timings.Sum() / times}");
        }

Closes #626 (closed)