Add extra trace attributes from downward API

This allows us to specify extra trace attribute key-value pairs from the downward API without needing to pull from the pods annotations or labels. This lets us keep the proxy decoupled from k8s concepts.

Signed-off-by: Scott Fleener <[email protected]>

jaeger/injector/mutator/patch.go

@@ -46,6 +46,14 @@ const tpl = `[
       "value": "{{.CollectorSvcAccount}}.serviceaccount.identity.{{.LinkerdNamespace}}.{{.ClusterDomain}}"
     }
   },
+  {
+    "op": "add",
+    "path": "/spec/{{.ProxyPath}}/env/-",
+    "value": {
+      "name": "LINKERD2_PROXY_TRACE_EXTRA_ATTRIBUTES",
+      "value": "k8s.pod.uid=$(_pod_uid)\nk8s.container.name=$(_pod_containerName)"
+    }
+  },
   {
     "op": "add",
     "path": "/spec/{{.ProxyPath}}/volumeMounts/-",