[lgtm] tag cfg/ folder as generated, to prevent lgtm python detection (#99)

#### Why I did it
Prevent lgtm python detection

#### How I did it
Tag cfg folder as generated

Author: qiluo-msft

lgtm.yml

@@ -1,5 +1,9 @@
-extraction:
-  go:
-    before_index:
-    - "git clone https://github.com/Azure/sonic-mgmt-common.git"
-    - "sed -i 's@replace github.com/Azure/sonic-mgmt-common => ../sonic-mgmt-common@replace github.com/Azure/sonic-mgmt-common => ./sonic-mgmt-common@g' go.mod"
+path_classifiers:
+  generated:
+    - cfg
+
+extraction:
+  go:
+    before_index:
+    - "git clone https://github.com/Azure/sonic-mgmt-common.git"
+    - "sed -i 's@replace github.com/Azure/sonic-mgmt-common => ../sonic-mgmt-common@replace github.com/Azure/sonic-mgmt-common => ./sonic-mgmt-common@g' go.mod"