feat(nimbus): Rollout badge (#12659)

Because

- If the type is rollout, then we show a badge on top of the summary
page to show that it is a rollout.

This commit

- Adds the badge on the new summary page indicating if it's a rollout

Fixes #1265
<img width="1329" alt="Screenshot 2025-05-20 at 2 47 23 PM"
src="https://github.com/user-attachments/assets/4fb7f213-1008-4c25-817c-c712f1006323"
/>
8

Author: yashikakhurana

experimenter/experimenter/nimbus_ui_new/templates/nimbus_experiments/experiment_base.html

@@ -13,6 +13,7 @@ <h4 class="mb-0">{{ experiment.name }}</h4>
       {% if experiment.is_archived %}
         <span class="badge rounded-pill bg-danger" id="archive-badge">Archived</span>
       {% endif %}
+      {% if experiment.is_rollout %}<span class="badge rounded-pill bg-primary" id="rollout-badge">Rollout</span>{% endif %}
       <span class="{{ experiment.qa_status_badge_class }}">
         QA Status: {{ experiment.qa_status|default:"Not Set"|title }}
       </span>