Define container environment variables using Secret data (#13800)

* Example for injecting single secret as env variable

Define a container environment variable with data from a single Secret

* Env variable using secret data

* Update pod-single-secret-env-variable.yaml

* Adding example for multiple env variable using secrets

Adding example for multiple env variables using secrets

* Create pod-secret-envFrom.yaml

* Update pod-multiple-secret-env-variable.yaml

* Update pod-multiple-secret-env-variable.yaml

* Update pod-multiple-secret-env-variable.yaml

* Update pod-single-secret-env-variable.yaml

* Update pod-multiple-secret-env-variable.yaml

* Update pod-single-secret-env-variable.yaml

* Different ways to add env variable using secret

Adding different ways to add env variable in pod using secret

* Correcting formatting issues

Correcting formatting issues

* Correcting format issue

content/en/examples/pods/inject/pod-multiple-secret-env-variable.yaml

@@ -0,0 +1,19 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: envvars-multiple-secrets
+spec:
+  containers:
+  - name: envars-test-container
+    image: nginx
+    env:
+    - name: BACKEND_USERNAME
+      valueFrom:
+        secretKeyRef:
+          name: backend-user
+          key: backend-username
+    - name: DB_USERNAME
+      valueFrom:
+        secretKeyRef:
+          name: db-user
+          key: db-username

content/en/examples/pods/inject/pod-secret-envFrom.yaml

@@ -0,0 +1,11 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: envfrom-secret
+spec:
+  containers:
+  - name: envars-test-container
+    image: nginx
+    envFrom:
+    - secretRef:
+        name: test-secret

content/en/examples/pods/inject/pod-single-secret-env-variable.yaml

@@ -0,0 +1,14 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: env-single-secret
+spec:
+  containers:
+  - name: envars-test-container
+    image: nginx
+    env:
+    - name: SECRET_USERNAME
+      valueFrom:
+        secretKeyRef:
+          name: backend-user
+          key: backend-username