github: Switch to yaml issue templates

These provide more flexibility and can be designed to extract more
information from users when submitting issues.

.github/ISSUE_TEMPLATE/gui_issue.yml

@@ -0,0 +1,18 @@
+name: Issue or feature request related to the GUI
+description: Any report, issue or feature request related to the GUI
+labels: [GUI]
+body:
+- type: checkboxes
+  id: acknowledgement
+  attributes:
+    label: Issues, reports or feature requests related to the GUI should be opened directly on the GUI repo
+    description: https://github.com/bitcoin-core/gui/issues/
+    options:
+      - label: I still think this issue should be opened here
+        required: true
+- type: textarea
+  id: gui-request
+  attributes:
+    label: Report
+  validations:
+    required: true