Update issue templates to support issue types and allow blank issues (for internal use)

.github/ISSUE_TEMPLATE/config.yml

@@ -1,4 +1,4 @@
-blank_issues_enabled: false
+blank_issues_enabled: true
 contact_links:
   - name: DAVx⁵ Community Support
     url: https://github.com/bitfireAT/davx5-ose/discussions

.github/ISSUE_TEMPLATE/qualified-bug.yml

@@ -1,5 +1,6 @@
 name: Qualified Bug Report
-description: "[Developers only] For qualified bug reports. (Use Discussions if unsure.)"
+description: "For qualified bug reports. (Use Discussions if unsure.)"
+type: bug
 labels: ["bug"]
 body:
   - type: checkboxes

.github/ISSUE_TEMPLATE/qualified-feature.yml

@@ -1,5 +1,6 @@
 name: Qualified Feature Request
-description: "[Developers only] For qualified feature requests. (Use Discussions if unsure.)"
+description: "For qualified feature requests. (Use Discussions if unsure.)"
+type: feature
 labels: ["enhancement"]
 body:
   - type: checkboxes