Adds configuration for codeql to disable obsolete method check (#197)

Author: dnperfors

.github/codeql-config.yml

@@ -0,0 +1,5 @@
+name: "TestableHttpClient codeql configuration"
+
+query-filters:
+  - exclude:
+      id: cs/call-to-obsolete-method

.github/workflows/codeql.yml

@@ -33,6 +33,7 @@ jobs:
       with:
         queries: security-and-quality
         languages: csharp
+        config-file: ./.github/codeql-config.yml
     - name: Build source code
       run: dotnet build --configuration Release --framework net6.0
     - name: Perform CodeQL Analysis