Reuse HttpClient and fix the wrong TLS and Proxy settings during MinioClient creation

[ebozduman]

Socket/Memory leak issue was addressed before, but there was a case where we were not using HttpHandler when MinioClient is created with no args.
Also adds a functional test for socket/memory leak issue.

[ebozduman]

Running dotnet regitlint --fail-on-diff for the build issue

[harshavardhana]

Running dotnet regitlint --fail-on-diff for the build issue

You need fix, your formatting is all wrong for a .Net project source. Also you can't remove TLS skip for verification. Or you would have to trust the certs in CI/CD

[ebozduman]

OK. I'll add TLS back.

About formatting:
I use VisualStudio as my editor and I've disabled format on save setting, but it still forces format changes. I'll check it in again. I'll also make sure I manually run dotnet regitlint before pushing the changes going forward.

[harshavardhana]

Some reviews

[ebozduman]

Implemented review comments and removed the socket/memory test per team decision.

Marked the parameterized construction method, MinioClient(HttpClient httpClient), obsolete. If user has this method used in his/her code, then s/he will see a message similar to the following warning message:

.../Minio.Functional.Tests/Program.cs(69,27): warning CS0618: 'MinioClient.MinioClient(HttpClient)' is obsolete: 
'Use MinioClient() and Builder method .WithHttpClient(httpClient)' [.../Minio.Functional.Tests/Minio.Functional.Tests.csproj]

[harshavardhana]

I am not sure what is the bug fix here? @ebozduman - can you please explain?

[ebozduman]

Sorry for the confusion.
Things changed in time and the title and what has changed diverged.

TLDR: This PR will make the last 3 test cases reuse the existing HttpClient instance and fix the wrong TLS and Proxy settings when creating an instance of MinioClient.

Some more explanations:
After the original socket leakage problem is addressed (too many HttpClient instances were created instead of reusing the existing one), I wanted to create a test for it and add some extra clean up for the 3 tests that were still creating their own HttpClient (and MinioClient) instances. Those 3 tests depended on DownloadObjectAsync and UploadObjectAsync methods.

In the meantime, I discussed with Bala and like the other SDKs, we've decided a functional test for socket leakage is not necessary.

I also got the reviews from you for the unnecessary HttpHandler creation which was turning off TLS and the review about the proxy setting that causes not honoring local system proxies.

So, this PR will make the last 3 test cases to reuse the existing HttpClient instance and fix the wrong TLS and Proxy settings.
I'll change the title to reflect the correct definition of these changes.