Documenting how to use EvenPodsSpread feature (#15514)

* Documenting how to use EvenPodsSpread feature

* address comments

* address comments

* address sftim's comments

* move to folder workloads/pods

* address comments

* move yamls to examples folder and reference back in the document

* Link from scheduling to topology spread constraints

content/en/examples/pods/topology-spread-constraints/one-constraint-with-nodeaffinity.yaml

@@ -0,0 +1,26 @@
+kind: Pod
+apiVersion: v1
+metadata:
+  name: mypod
+  labels:
+    foo: bar
+spec:
+  topologySpreadConstraints:
+  - maxSkew: 1
+    topologyKey: zone
+    whenUnsatisfiable: DoNotSchedule
+    labelSelector:
+      matchLabels:
+        foo: bar
+  affinity:
+    nodeAffinity:
+      requiredDuringSchedulingIgnoredDuringExecution:
+        nodeSelectorTerms:
+        - matchExpressions:
+          - key: zone
+            operator: NotIn
+            values:
+            - zoneC
+  containers:
+  - name: pause
+    image: k8s.gcr.io/pause:3.1

content/en/examples/pods/topology-spread-constraints/one-constraint.yaml

@@ -0,0 +1,17 @@
+kind: Pod
+apiVersion: v1
+metadata:
+  name: mypod
+  labels:
+    foo: bar
+spec:
+  topologySpreadConstraints:
+  - maxSkew: 1
+    topologyKey: zone
+    whenUnsatisfiable: DoNotSchedule
+    labelSelector:
+      matchLabels:
+        foo: bar
+  containers:
+  - name: pause
+    image: k8s.gcr.io/pause:3.1

content/en/examples/pods/topology-spread-constraints/two-constraints.yaml

@@ -0,0 +1,23 @@
+kind: Pod
+apiVersion: v1
+metadata:
+  name: mypod
+  labels:
+    foo: bar
+spec:
+  topologySpreadConstraints:
+  - maxSkew: 1
+    topologyKey: zone
+    whenUnsatisfiable: DoNotSchedule
+    labelSelector:
+      matchLabels:
+        foo: bar
+  - maxSkew: 1
+    topologyKey: node
+    whenUnsatisfiable: DoNotSchedule
+    labelSelector:
+      matchLabels:
+        foo: bar
+  containers:
+  - name: pause
+    image: k8s.gcr.io/pause:3.1