Remove requirement for certificate authority and certificate authority data in kubeconfig. (#222)

* Remove requirement for certificate authority data in kubeconfig.

* Update src/KubernetesClient/KubernetesClientConfiguration.ConfigFile.cs

Update casing of `URL` at @itowlson suggestion.

Co-Authored-By: twitchax <twitchax@gmail.com>

tests/KubernetesClient.Tests/KubernetesClientConfigurationTests.cs

@@ -70,17 +70,6 @@ namespace k8s.Tests
             Assert.Equal(File.ReadAllText("assets/client-key-data.txt"), cfg.ClientCertificateKeyData);
         }
 
-        /// <summary>
-        ///     Checks that a KubeConfigException is thrown when no certificate-authority-data is set and user do not require tls
-        ///     skip
-        /// </summary>
-        [Fact]
-        public void CheckClusterTlsCorrectness()
-        {
-            var fi = new FileInfo("assets/kubeconfig.tls-no-skip-error.yml");
-            Assert.Throws<KubeConfigException>(() => KubernetesClientConfiguration.BuildConfigFromConfigFile(fi));
-        }
-
         /// <summary>
         ///     Checks that a KubeConfigException is thrown when no certificate-authority-data is set and user do not require tls
         ///     skip

tests/KubernetesClient.Tests/assets/kubeconfig.tls-no-skip-error.yml

@@ -1,25 +0,0 @@
-# Sample file based on https://kubernetes.io/docs/tasks/access-application-cluster/authenticate-across-clusters-kubeconfig/
-# WARNING: File includes minor fixes
----
-current-context: federal-context
-apiVersion: v1
-clusters:
-- cluster:
-    server: http://cow.org:8080
-  name: cow-cluster
-- cluster:
-    # certificate-authority: path/to/my/cafile
-    server: https://horse.org:4443
-  name: horse-cluster
-contexts:
-- context:
-    cluster: horse-cluster
-    namespace: chisel-ns
-    user: green-user
-  name: federal-context
-kind: Config
-users:
-- name: green-user
-  user:
-    client-certificate: assets/client.crt
-    client-key: assets/client.key