adding Sidecar Containers alpha feature

Signed-off-by: Matthias Bertschy <matthias.bertschy@gmail.com>

content/en/docs/concepts/workloads/pods/_index.md

@@ -112,7 +112,9 @@ that updates those files from a remote source, as in the following diagram:
 
 {{< figure src="/images/docs/pod.svg" alt="Pod creation diagram" class="diagram-medium" >}}
 
-Some Pods have {{< glossary_tooltip text="init containers" term_id="init-container" >}} as well as {{< glossary_tooltip text="app containers" term_id="app-container" >}}. Init containers run and complete before the app containers are started.
+Some Pods have {{< glossary_tooltip text="init containers" term_id="init-container" >}} as well as {{< glossary_tooltip text="app containers" term_id="app-container" >}}. By default, init containers run and complete before the app containers are started.
+However an new feature called SidecarContainers (alpha in 1.28) allows specifying
+a restartPolicy=Always to init containers, enabling an solution to officially support the sidecar pattern.
 
 Pods natively provide two kinds of shared resources for their constituent containers:
 [networking](#pod-networking) and [storage](#pod-storage).

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

@@ -192,6 +192,7 @@ For a reference to old feature gates that are removed, please refer to
 | `SecurityContextDeny` | `false` | Alpha | 1.27 | |
 | `ServiceNodePortStaticSubrange` | `false` | Alpha | 1.27 | 1.27 |
 | `ServiceNodePortStaticSubrange` | `true` | Beta | 1.28 | |
+| `SidecarContainers` | `false` | Beta | 1.28 | |
 | `SizeMemoryBackedVolumes` | `false` | Alpha | 1.20 | 1.21 |
 | `SizeMemoryBackedVolumes` | `true` | Beta | 1.22 | |
 | `StableLoadBalancerNodeGet` | `true` | Beta | 1.27 | |
@@ -753,4 +754,4 @@ Each feature gate is designed for enabling/disabling a specific feature:
   feature, you will also need to enable any associated API resources.
   For example, to enable a particular resource like
   `storage.k8s.io/v1beta1/csistoragecapacities`, set `--runtime-config=storage.k8s.io/v1beta1/csistoragecapacities`.
-  See [API Versioning](/docs/reference/using-api/#api-versioning) for more details on the command line flags.
+  See [API Versioning](/docs/reference/using-api/#api-versioning) for more details on the command line flags.