Merge pull request #38445 from brendandburns/configmap2

Automatic merge from submit-queue (batch tested with PRs 38445, 40292)

Add the ability to edit fields within a config map.

Addresses part of https://github.com/kubernetes/kubernetes/issues/36222

Example command:

```console
$ kubectl edit configmap foo --config-map-data=bar
```

Will open the data element named `bar` in the `ConfigMap` named `foo` in `$EDITOR`, the edited contents are then updated back to the config map.

@kubernetes/sig-cli 

```release-note
Add a special purpose tool for editing individual fields in a ConfigMap with kubectl
```

hack/verify-flags/known-flags.txt

@@ -97,6 +97,7 @@ concurrent-resource-quota-syncs
 concurrent-serviceaccount-token-syncs
 concurrent-service-syncs
 config-map
+config-map-data
 config-map-namespace
 config-sync-period
 configure-cloud-routes