Backport PR #2868 on branch 1.10.x (Allow blank issues) (#2882)

Co-authored-by: Isaac Virshup <ivirshup@gmail.com>

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,8 @@
-blank_issues_enabled: false
+blank_issues_enabled: true
 contact_links:
   - name: Scanpy Community Forum
     url: https://discourse.scverse.org/
     about: If you have questions about “How to do X”, please ask them here.
+  - name: Blank issue
+    url: https://github.com/scverse/scanpy/issues/new
+    about: For things that don't quite fit elsewhere. Please note that other templates should be used in most cases – this is mainly for use by the developers.