Add pod name to context token and logging (#11532)

When the destination controller logs about receiving or sending messages to a data plane proxy, there is no information in the log about which data plane pod it is communicating with.  This can make it difficult to diagnose issues which span the data plane and control plane.

We add a `pod` field to the context token that proxies include in requests to the destination controller.  We add this pod name to the logging context so that it shows up in log messages.  In order to accomplish this, we had to plumb through logging context in a few places where it previously had not been.  This gives us a more complete logging context and more information in each log message.

An example log message with this fuller logging context is:

```
time="2023-10-24T00:14:09Z" level=debug msg="Sending destination add: add:{addrs:{addr:{ip:{ipv4:183762990}  port:8080}  weight:10000  metric_labels:{key:\"control_plane_ns\"  value:\"linkerd\"}  metric_labels:{key:\"deployment\"  value:\"voting\"}  metric_labels:{key:\"pod\"  value:\"voting-7475cb974c-2crt5\"}  metric_labels:{key:\"pod_template_hash\"  value:\"7475cb974c\"}  metric_labels:{key:\"serviceaccount\"  value:\"voting\"}  tls_identity:{dns_like_identity:{name:\"voting.emojivoto.serviceaccount.identity.linkerd.cluster.local\"}}  protocol_hint:{h2:{}}}  metric_labels:{key:\"namespace\"  value:\"emojivoto\"}  metric_labels:{key:\"service\"  value:\"voting-svc\"}}" addr=":8086" component=endpoint-translator context-ns=emojivoto context-pod=web-767f4484fd-wmpvf remote="10.244.0.65:52786" service="voting-svc.emojivoto.svc.cluster.local:8080"
```

Note the `context-pod` field.

Additionally, we have tested this when no pod field is included in the context token (e.g. when handling requests from a pod which does not yet add this field) and confirmed that the `context-pod` log field is empty, but no errors occur.

Signed-off-by: Alex Leong <alex@buoyant.io>

charts/partials/templates/_proxy.tpl

@@ -100,7 +100,7 @@ env:
 {{ end -}}
 - name: LINKERD2_PROXY_DESTINATION_CONTEXT
   value: |
-    {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)"}
+    {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)", "pod":"$(_pod_name)"}
 - name: _pod_sa
   valueFrom:
     fieldRef:

cli/cmd/testdata/inject-filepath/expected/injected_nginx.yaml

@@ -80,7 +80,7 @@ spec:
           value: 25,587,3306,4444,5432,6379,9300,11211
         - name: LINKERD2_PROXY_DESTINATION_CONTEXT
           value: |
-            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)"}
+            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)", "pod":"$(_pod_name)"}
         - name: _pod_sa
           valueFrom:
             fieldRef:

cli/cmd/testdata/inject-filepath/expected/injected_nginx_redis.yaml

@@ -80,7 +80,7 @@ spec:
           value: 25,587,3306,4444,5432,6379,9300,11211
         - name: LINKERD2_PROXY_DESTINATION_CONTEXT
           value: |
-            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)"}
+            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)", "pod":"$(_pod_name)"}
         - name: _pod_sa
           valueFrom:
             fieldRef:
@@ -294,7 +294,7 @@ spec:
           value: 25,587,3306,4444,5432,6379,9300,11211
         - name: LINKERD2_PROXY_DESTINATION_CONTEXT
           value: |
-            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)"}
+            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)", "pod":"$(_pod_name)"}
         - name: _pod_sa
           valueFrom:
             fieldRef:

cli/cmd/testdata/inject-filepath/expected/injected_redis.yaml

@@ -80,7 +80,7 @@ spec:
           value: 25,587,3306,4444,5432,6379,9300,11211
         - name: LINKERD2_PROXY_DESTINATION_CONTEXT
           value: |
-            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)"}
+            {"ns":"$(_pod_ns)", "nodeName":"$(_pod_nodeName)", "pod":"$(_pod_name)"}
         - name: _pod_sa
           valueFrom:
             fieldRef: