feat(label_new_contributor): link to the 'why is my PR not on the queue' dashboard (#35583)

Follow-up to #35109, discussed [also on zulip](https://leanprover.zulipchat.com/#narrow/channel/113488-general/topic/Adding.20new.20contributor.20comment.20on.20PR/near/573405975).

Author: grunweg

.github/workflows/label_new_contributor.yml

@@ -106,7 +106,7 @@ jobs:
             ## Welcome new contributor!
             Thank you for contributing to Mathlib! If you haven't done so already, please review our [contribution guidelines](https://leanprover-community.github.io/contribute/index.html), as well as the [style guide](https://leanprover-community.github.io/contribute/style.html) and [naming conventions](https://leanprover-community.github.io/contribute/naming.html).
 
-            We use a [review queue](https://leanprover-community.github.io/queueboard/review_dashboard.html) to manage reviews. If your PR does not appear there, it is probably because it is not successfully building (i.e., it doesn't have a green checkmark), has the `awaiting-author` tag, or another reason described in the [Lifecycle of a PR](https://leanprover-community.github.io/contribute/index.html#lifecycle-of-a-pr).
+            We use a [review queue](https://leanprover-community.github.io/queueboard/review_dashboard.html) to manage reviews. If your PR does not appear there, it is probably because it is not successfully building (i.e., it doesn't have a green checkmark), has the `awaiting-author` tag, or another reason described in the [Lifecycle of a PR](https://leanprover-community.github.io/contribute/index.html#lifecycle-of-a-pr). The review dashboard has [a dedicated webpage](https://leanprover-community.github.io/queueboard/on_the_queue.html?search=${{ github.event.pull_request.number }}) which shows whether your PR is on the review queue, and (if not), why.
 
             If you haven't already done so, please come to [https://leanprover.zulipchat.com/](https://leanprover.zulipchat.com/), introduce yourself, and mention your new PR.