fix: update configuration files to use YAML format and adjust references in deployment

deployment.yaml

@@ -43,9 +43,9 @@ spec:
             - name: config-volume
               mountPath: /config
             - name: helloapp-test-key
-              mountPath: /certs
+              mountPath: /certs/test.key
           command: ["/helloapp"]
-          args: ["-f", "/config/.linux-config.json"]
+          args: ["-f", "/config/.linux-config.yaml"]
       volumes:
         - name: config-volume
           configMap:
@@ -60,12 +60,8 @@ metadata:
   name: k8s-example-config
   namespace: helloapp
 data:
-  .linux-config.json: |
-    {
-      "server": {
-        "port": 8800
-      },
-      "certs": {
-        "testKeyPath": "./certs/test.key"
-      }
-    }
+  .linux-config.yaml: |
+    server:
+      port: 8800
+    certs:
+      testKeyPath: /certs/test.key