Configure LGTM (#2723)

Exclude the plugins folder since it slows down the scan a lot

.lgtm.yml

@@ -0,0 +1,14 @@
+# https://lgtm.com/help/lgtm/customizing-file-classification
+path_classifiers:
+  plugins:
+    - plugins/
+
+extraction:
+  javascript:
+    # The `index` step extracts information from the files in the codebase.
+    index:
+      # Specify a list of files and folders to exclude from extraction.
+      filters:
+        - exclude: plugins/
+      exclude:
+        - plugins/