Report namespace and pod name when port-forward fails (#5504)

Subject
Related to issue #5457 

Problem
Linkerd only reports the local port and the remote port whenever port-forwarding fails.
Linkerd could print out namespace and port if port-forwarding fails instead of just at the error state and then force users to collate the port themselves

Solution
Linkerd needs to print the namespace and the pod name.
- [x] Add two new string variables namespace and podName in `struct PortForward`
- [x] assign the values to the variables when a new Instance is being created in `func NewPortForward()`
run() function propagates the errors that occurred while port-forwarding
- [x] Format the error being returned by `ForwardPorts()` from client-go using `fmt.Errorf()` and add `namespace` and `podName` as suffix and return error

The error is being returned by ForwardPorts() from client-go https://github.com/kubernetes/client-go/blob/master/tools/portforward/portforward.go#L188

Fixes #5457 

Signed-off-by: Piyush Singariya <piyushsingariya@gmail.com>

pkg/k8s/portforward.go

@@ -25,6 +25,8 @@ type PortForward struct {
 	method     string
 	url        *url.URL
 	host       string
+	namespace  string
+	podName    string
 	localPort  int
 	remotePort int
 	emitLogs   bool
@@ -140,6 +142,8 @@ func newPortForward(
 		method:     "POST",
 		url:        req.URL(),
 		host:       host,
+		namespace:  namespace,
+		podName:    podName,
 		localPort:  localPort,
 		remotePort: remotePort,
 		emitLogs:   emitLogs,
@@ -172,7 +176,12 @@ func (pf *PortForward) run() error {
 		return err
 	}
 
-	return fw.ForwardPorts()
+	err = fw.ForwardPorts()
+	if err != nil {
+		err = fmt.Errorf("%s for %s/%s", err, pf.namespace, pf.podName)
+		return err
+	}
+	return nil
 }
 
 // Init creates and runs a port-forward connection.