Disable blank issue option in Github UI (#11701)

We're still getting bug reports circumventing the bug report template
and omitting informations.

Blank issue (aka, not using the form templates) can still be created
using the gh cli, the API, etc. This only disable the possibility in the
Web UI.

.github/ISSUE_TEMPLATE/config.yml

 ---
+blank_issues_enabled: false
 contact_links:
   - name: Support Request
     url: https://kubernetes.slack.com/channels/kubespray