docs: Update issue templates (#427)

.github/ISSUE_TEMPLATE/FEATURE_REQUEST.yml

@@ -3,6 +3,13 @@ description: Suggest an idea for improving the container
 title: "[Feature]: "
 labels: ["enhancement"]
 body:
+  - type: checkboxes
+    attributes:
+      label: Is there an existing feature request for this?
+      description: Please search to see if the feature request already exists.
+      options:
+      - label: I have searched the existing feature requests
+        required: true
   - type: textarea
     id: problem
     attributes: