YAML based REST tests.

=== Good practices

==== What kind of tests should I write?

Unit tests are the preferred way to test some functionality: most of the time
they are simpler to understand, more likely to reproduce, and unlikely to be
affected by changes that are unrelated to the piece of functionality that is
being tested.

The reason why `ESSingleNodeTestCase` exists is that all our components used to

 *
 * <p><b>Warning:</b> This class deals only with {@code char} values, that is, <a
 * href="http://www.unicode.org/glossary/#BMP_character">BMP characters</a>. It does not understand
 * <a href="http://www.unicode.org/glossary/#supplementary_code_point">supplementary Unicode code
 * points</a> in the range {@code 0x10000} to {@code 0x10FFFF} which includes the majority of

 *
 * <p><b>Warning:</b> This class deals only with {@code char} values, that is, <a
 * href="http://www.unicode.org/glossary/#BMP_character">BMP characters</a>. It does not understand
 * <a href="http://www.unicode.org/glossary/#supplementary_code_point">supplementary Unicode code
 * points</a> in the range {@code 0x10000} to {@code 0x10FFFF} which includes the majority of

  * You *MUST* set `--anonymous-auth=false` flag on your kube-apiserver unless you are a developer testing this feature and understand it.
  If you do not, you risk allowing unauthorized users to access your apiserver.
  * You *MUST* set `--anonymous-auth=false` flag on your federation apiserver unless you are a developer testing this feature and understand it.
    If you do not, you risk allowing unauthorized users to access your federation apiserver.

- Added metrics `authentication_attempts` that can be used to understand the attempts of authentication. ([#81509](https://github.com/kubernetes/kubernetes/pull/81509), [@RainbowMango](https://github.com/RainbowMango))

- Kube-apiserver: Added metrics `authentication_latency_seconds` that can be used to understand the latency of authentication. ([#82409](https://github.com/kubernetes/kubernetes/pull/82409), [@RainbowMango](https://github.com/RainbowMango))

## Major Themes

- **Simplified User Experience**
  - Easier to get a cluster up and running (eg: `kubeadm`, intra-cluster bootstrapping)
  - Easier to understand a cluster (eg: API audit logs, server-based API defaults)
- **Stateful Application Support**
  - Enhanced persistence capabilities (eg: `StorageClasses`, new volume plugins)

deployments`) and be called when any other version of that resource is modified (for example `extensions/v1beta1 deployments`). This allows new versions of a resource to be handled by admission webhooks without needing to update every webhook to understand the new version. See the API documentation for the `matchPolicy: Equivalent` option in MutatingWebhookConfiguration and ValidatingWebhookConfiguration types. ([#78135](https://github.com/kubernetes/kubernetes/pull/78135), [@liggitt](https://github.com/liggitt))...

- Adds the ability to pass --strict-transport-security-directives to the kube-apiserver to set the HSTS header appropriately.  Be sure you understand the consequences to browsers before setting this field. ([#96502](https://github.com/kubernetes/kubernetes/pull/96502), [@249043822](https://github.com/249043822)) [SIG Auth]

### Documentation

- Added a new internal metric `kubelet_first_network_pod_start_sli_duration_second` in the kubelet that allowed developers to understand the source of the latency problems on node startups.
   ([#121720](https://github.com/kubernetes/kubernetes/pull/121720), [@aojea](https://github.com/aojea))