Update GitHub issue, discussion templates (#445)

* Update GitHub issue templates to match axum's
* Use axum's Q&A discussion template

.github/DISCUSSION_TEMPLATE/q-a.yml

@@ -0,0 +1,21 @@
+body:
+  - type: textarea
+    attributes:
+      label: Summary
+      description: 'Your question:'
+    validations:
+      required: true
+  - type: input
+    attributes:
+      label: tower-http version
+      description: 'Please look it up in `Cargo.lock`, or as described below'
+    validations:
+      required: true
+  - type: markdown
+    attributes:
+      value: |
+        > If you have `jq` installed, you can look up the version by running
+        >
+        > ```bash
+        > cargo metadata --format-version=1 | jq -r '.packages[] | select(.name == "tower-http") | .version'
+        > ```

.github/ISSUE_TEMPLATE/bug_report.md

@@ -4,14 +4,16 @@ about: If something isn't working as expected 🤔.
 
 ---
 
-## Bug Report
-
 <!--
 Thank you for reporting an issue.
 
 Please fill in as much of the template below as you're able.
 -->
 
+- [ ] I have looked for existing issues (including closed) about this
+
+## Bug Report
+
 ### Version
 
 <!--

.github/ISSUE_TEMPLATE/feature_request.md

@@ -4,6 +4,8 @@ about: I have a suggestion (and may want to implement it 🙂)!
 
 ---
 
+- [ ] I have looked for existing issues (including closed) about this
+
 ## Feature Request
 
 ### Motivation