Bootstrap PR-based benchmarks (#132717)

Author: gbanasiak

.buildkite/pull-requests.json

@@ -15,6 +15,19 @@
       "trigger_comment_regex": "(run\\W+elasticsearch-ci.+)|(^\\s*((buildkite|@elastic(search)?machine)\\s*)?test\\s+this(\\s+please)?)",
       "cancel_intermediate_builds": true,
       "cancel_intermediate_builds_on_comment": false
+    },
+    {
+      "enabled": true,
+      "pipeline_slug": "elasticsearch-performance-esbench-pr",
+      "allow_org_users": true,
+      "allowed_repo_permissions": [
+        "admin",
+        "write"
+      ],
+      "set_commit_status": false,
+      "build_on_commit": false,
+      "build_on_comment": true,
+      "trigger_comment_regex": "^(buildkite|@elastic(search)?machine) benchmark this with (?<benchmark>\\w+)( please)?$"
     }
   ]
 }