chore: edit issue templates to encourage GitHub account linking for Cloud customers (#12391)

To help us better identify and prioritize issues and requests from our
paying customers, this PR adds a quick callout to the top of our GitHub
issue templates. It prompts users with active ZITADEL Cloud
subscriptions to link their GitHub accounts to their Cloud accounts via
the Customer Portal.

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

.github/ISSUE_TEMPLATE/BUG_REPORT.yaml

@@ -8,6 +8,8 @@ body:
     value: |
       Thanks for taking the time to fill out this bug report!  
       Learn more in our [contribution guide](https://github.com/zitadel/zitadel/blob/main/CONTRIBUTING.md#product-management) on how we will process your issue.
+
+      **To help us better prioritize your bug report**, if you have an active ZITADEL Cloud subscription, please [link your GitHub account to your Cloud account in the Customer Portal](https://zitadel.com/admin/support).
 - type: checkboxes
   id: preflight
   attributes:

.github/ISSUE_TEMPLATE/docs.yaml

@@ -7,6 +7,8 @@ body:
     attributes:
       value: |
         Thanks for taking the time to fill out this issue.
+
+        **To help us better prioritize your issue**, if you have an active ZITADEL Cloud subscription, please [link your GitHub account to your Cloud account in the Customer Portal](https://zitadel.com/admin/support).
   - type: checkboxes
     id: preflight
     attributes:

.github/ISSUE_TEMPLATE/enhancement.yaml

@@ -5,7 +5,9 @@ body:
   - type: markdown
     attributes:
       value: |
-        Thanks for taking the time to fill out this proposal / feature reqeust
+        Thanks for taking the time to fill out this proposal / feature request.
+
+        **To help us better prioritize**, if you have an active ZITADEL Cloud subscription, please [link your GitHub account to your Cloud account in the Customer Portal](https://zitadel.com/admin/support).
   - type: checkboxes
     id: preflight
     attributes: