Separating tasks from Secret concept

There are many contents in the (*very big*) Secret concept page which
are actually tasks. This PR proposes a separation of some contents
into separate tasks, so that we have a (hopefully) better organization
of the content and we make room for improvement to the concept itself.

Note that the creation of the `configmap-secret` directory (instead of
`secret`) is an intent to create a folder for both ConfigMap and Secret,
both of which are about configurations though there are quite some
differences between them.

content/en/docs/tasks/configmap-secret/managing-secret-using-kubectl.md

@@ -0,0 +1,157 @@
+---
+title: Managing Secret using `kubectl`
+content_type: task
+weight: 10
+description: Creating Secret objects using kubectl command line.
+---
+
+<!-- overview -->
+
+## {{% heading "prerequisites" %}}
+
+{{< include "task-tutorial-prereqs.md" >}}
+
+<!-- steps -->
+
+## Create a Secret
+
+A `Secret` can contain user credentials required by Pods to access a database.
+For example, a database connection string consists of a username and password.
+You can store the username in a file `./username.txt` and the password in a
+file `./password.txt` on your local machine.
+
+```shell
+echo -n 'admin' > ./username.txt
+echo -n '1f2d1e2e67df' > ./password.txt
+```
+
+The `-n` flag in the above two commands ensures that the generated files will
+not contain an extra newline character at the end of the text. This is
+important because when `kubectl` reads a file and encode the content into
+base64 string, the extra newline character gets encoded too.
+
+The `kubectl create secret` command packages these files into a Secret and creates
+the object on the API server.
+
+```shell
+kubectl create secret generic db-user-pass \
+  --from-file=./username.txt \
+  --from-file=./password.txt
+```
+
+The output is similar to:
+
+```
+secret/db-user-pass created
+```
+
+Default key name is the filename. You may optionally set the key name using
+`--from-file=[key=]source`. For example:
+
+```shell
+kubectl create secret generic db-user-pass \
+  --from-file=username=./username.txt \
+  --from-file=password=./password.txt
+```
+
+You do not need to escape special characters in passwords from files
+(`--from-file`).
+
+You can also provide Secret data using the `--from-literal=<key>=<value>` tag.
+This tag can be specified more than once to provide multiple key-value pairs.
+Note that special characters such as `$`, `\`, `*`, `=`, and `!` will be
+interpreted by your [shell](https://en.wikipedia.org/wiki/Shell_(computing))
+and require escaping.
+In most shells, the easiest way to escape the password is to surround it with
+single quotes (`'`).  For example, if your actual password is `S!B\*d$zDsb=`,
+you should execute the command this way:
+
+```shell
+kubectl create secret generic dev-db-secret \
+  --from-literal=username=devuser \
+  --from-literal=password='S!B\*d$zDsb='
+```
+
+## Verify the Secret
+
+You can check that the secret was created:
+
+```shell
+kubectl get secrets
+```
+
+The output is similar to:
+
+```
+NAME                  TYPE                                  DATA      AGE
+db-user-pass          Opaque                                2         51s
+```
+
+You can view a description of the `Secret`:
+
+```shell
+kubectl describe secrets/db-user-pass
+```
+
+The output is similar to:
+
+```
+Name:            db-user-pass
+Namespace:       default
+Labels:          <none>
+Annotations:     <none>
+
+Type:            Opaque
+
+Data
+====
+password.txt:    12 bytes
+username.txt:    5 bytes
+```
+
+The commands `kubectl get` and `kubectl describe` avoid showing the contents
+of a `Secret` by default. This is to protect the `Secret` from being exposed
+accidentally to an onlooker, or from being stored in a terminal log.
+
+## Decoding the Secret  {#decoding-secret}
+
+To view the contents of the Secret we just created, you can run the following
+command:
+
+```shell
+kubectl get secret db-user-pass -o jsonpath='{.data}'
+```
+
+The output is similar to:
+
+```json
+{"password.txt":"MWYyZDFlMmU2N2Rm","username.txt":"YWRtaW4="}
+```
+
+Now you can decode the `password.txt` data:
+
+```shell
+echo 'MWYyZDFlMmU2N2Rm' | base64 --decode
+```
+
+The output is similar to:
+
+```
+1f2d1e2e67df
+```
+
+## Clean Up
+
+To delete the Secret you have just created:
+
+```shell
+kubectl delete secret db-user-pass
+```
+
+<!-- discussion -->
+
+## {{% heading "whatsnext" %}}
+
+- Read more about the [Secret concept](/docs/concepts/configuration/secret/)
+- Learn how to [manage Secret using config file](/docs/tasks/configmap-secret/managing-secret-using-config-file/)
+- Learn how to [manage Secret using kustomize](/docs/tasks/configmap-secret/managing-secret-using-kustomize/)