feat: add discussion templates for general category

Signed-off-by: Ryohsuke Mitsudome <[email protected]>

.github/DISCUSSION_TEMPLATE/general.yaml

@@ -0,0 +1,13 @@
+body:
+  - type: checkboxes
+    attributes:
+      label: Code of Conduct
+      options:
+        - label: I have read [CODE OF CONDUCT](https://github.com/autowarefoundation/autoware/blob/main/CODE_OF_CONDUCT.md) and [Support Guidelines](https://autowarefoundation.github.io/autoware-documentation/main/support/support-guidelines/#github-discussions) before creating this Discussion post.
+          required: true
+  - type: textarea
+    attributes:
+      label: Contents
+      description: Write your contents here
+    validations:
+      required: true