docs: add support option to 'new issue' choices (#3055)

config.yml mirrors
https://github.com/googleapis/google-cloud-java/blob/main/.github/ISSUE_TEMPLATE/config.yml

Author: burkedavison

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,4 @@
+contact_links:
+  - name: Google Cloud Support
+    url: https://cloud.google.com/support/
+    about: If you have a support contract with Google, please use the Google Cloud Support portal.