Add featuregate documentation and correct some doc suggestion

Author: rikatz

content/en/docs/concepts/services-networking/network-policies.md

@@ -257,7 +257,7 @@ The following restrictions apply when using this field:
 * As an alpha feature, this is disabled by default. To enable endPort field at a cluster level, you (or your cluster administrator) will need to enable the `NetworkPolicyEndPort` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) for the API server with `--feature-gates=NetworkPolicyEndPort=true,…`.
 * The `endPort` field must be equal than or greater to `port` field.
 * `endPort` can only be defined if `port` is also defined.
-* When using `endPort` field, the `port` field must be numeric.
+* Both ports must be numeric.
 
 {{< note >}}
 Your cluster must be using a {{< glossary_tooltip text="CNI" term_id="cni" >}} plugin that

content/en/docs/reference/command-line-tools-reference/feature-gates.md

@@ -135,6 +135,7 @@ different Kubernetes components.
 | `LocalStorageCapacityIsolation` | `true` | Beta | 1.10 | |
 | `LocalStorageCapacityIsolationFSQuotaMonitoring` | `false` | Alpha | 1.15 | |
 | `MixedProtocolLBService` | `false` | Alpha | 1.20 | |
+| `NetworkPolicyEndPort` | `false` | Alpha | 1.21 |  |
 | `NodeDisruptionExclusion` | `false` | Alpha | 1.16 | 1.18 |
 | `NodeDisruptionExclusion` | `true` | Beta | 1.19 | |
 | `NonPreemptingPriority` | `false` | Alpha | 1.15 | 1.18 |
@@ -657,6 +658,7 @@ Each feature gate is designed for enabling/disabling a specific feature:
   the volume mounter.
 - `MountPropagation`: Enable sharing volume mounted by one container to other containers or pods.
   For more details, please see [mount propagation](/docs/concepts/storage/volumes/#mount-propagation).
+- `NetworkPolicyEndPort`: Enable use of the field `endPort` in NetworkPolicy objects, allowing the selection of a port range instead of a single port.
 - `NodeDisruptionExclusion`: Enable use of the Node label `node.kubernetes.io/exclude-disruption`
   which prevents nodes from being evacuated during zone failures.
 - `NodeLease`: Enable the new Lease API to report node heartbeats, which could be used as a node health signal.