dashboard: Add link to retrigger failed pipelines

GitLab makes retrying failed jobs easy, but sometimes it's preferable to retrigger the whole pipeline from scratch for consistency, so let's make it more convenient by adding a dedicated button to each failure report.

templates/index.html.jinja2

@@ -295,6 +295,9 @@
           Upstream branch {{branch(package, report.branch)}} dropped
           {%- elif report.kind == "git-branch-pipeline-failed" -%}
           Pipeline failed on {{ branch(package, report.branch) }}: {{ pipeline(package, report.pipeline_web_url) }}
+            <a href="{{ package.git.web_url }}/pipelines/new?ref={{ report.branch.name|urlencode }}">
+              retrigger 🔁
+            </a>
           {%- elif report.kind == "git-branch-licensing-report-missing" -%}
           Missing licensing report on {{branch(package, report.branch)}}
           {%- elif report.kind == "git-branch-licensing-override" -%}