Update standard K8s version policy

The standard for the K8s version policy is updated in order to add the support period for Kubernetes versions into it. Since this is a bit contradictive with the K8s version recency, this part needed to be updated as well.

Signed-off-by: Hannes Baum <[email protected]>

Standards/scs-0210-v2-k8s-version-policy.md

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+---
+title: SCS K8S Version Policy
+type: Standard
+status: Draft
+track: KaaS
+---
+
+## Introduction
+
+The Kubernetes project maintains multiple release versions including their patched versions.
+In the project, the three most recent minor releases are actively maintained, with a fourth
+version being in development. As soon as a new minor version is officially released,
+the oldest version is dropped out of the support period.
+Kubernetes supports its releases for around 14 months. 12 of these are the standard
+support period. The remaining 2 months are the end-of-life support period for things like:
+
+- CVEs (under the advisement of the Security Response Committee)
+- dependency issues (including base image updates)
+- critical core component issues
+
+More information can be found under [Kubernetes Support Period].
+
+The Kubernetes release cycle is set around 4 months, which usually results in about
+**3 minor** releases per year [Kubernetes Release Cycle](https://kubernetes.io/releases/release/#the-release-cycle).
+
+Patches to these releases are provided monthly, with the exception of the first patch,
+which is usually provided 1-2 weeks after the initial release [Patch Release Cadence](https://kubernetes.io/releases/patch-releases/#cadence).
+
+## Motivation
+
+Kubernetes is a living, fast-paced project, which follows a pre-defined release cycle.
+This enables forward planning with regards to releases and patches, but also implies a
+necessity to upgrade to newer versions quickly, since these often include new features,
+important security updates or especially if a previous version falls out of the support
+period window.
+
+We want to achieve an up-to-date policy, meaning that providers should be mostly in
+sync with the upstream and don't fall behind the official Kubernetes releases.
+This is achievable, since new versions are released periodical on a well communicated
+schedule, enabling providers and users to set up processes around it.
+Being up to date ensures that security issues and bugs are addressed and new features
+are made available when using SCS compliant clusters.
+
+It is nevertheless important to at least support all Kubernetes versions that are still
+inside the support period, since users could depend on specific versions or may need
+longer to upgrade their workloads to a newer version.
+
+The standard therefore should provide a version recency policy as well as a support
+window period.
+
+## Decision
+
+In order to keep up-to date with the latest Kubernetes features, bug fixes and security improvements,
+the provided Kubernetes versions should be kept up to date with the upstream.
+
+- The latest minor version MUST be provided no later than 4 months after release.
+- The latest patch version MUST be provided no later than 1 week after release.
+- This time period MUST be even shorter for patches that target critical CVEs (CVSS >= 8).
+  It is RECOMMENDED to provide a new patch version in a 2 day time period after their release.
+- New versions MUST be tested before being rolled out on productive infrastructure;
+  at least the CNCF E2E tests should be passed beforehand.
+
+At the same time, providers must support Kubernetes versions at least as long as the
+official sources as mentioned in the [Kubernetes Support Period](https://kubernetes.io/releases/patch-releases/#support-period).
+
+- Kubernetes versions MUST be supported as long as the official sources support them.
+  The current support period can therefore be found in [Kubernetes Support Period].
+- It is RECOMMENDED to not support versions after this period in order to not encourage
+  usage of out-of-date versions.
+
+## Related Documents
+
+All documents regarding versioning, releases, etc. for the official Kubernetes projects can be found here:
+[Kubernetes Releases](https://kubernetes.io/releases/)
+[Kubernetes Support Period](https://kubernetes.io/releases/patch-releases/#support-period)
+[Kubernetes Release Cycle](https://kubernetes.io/releases/release/#the-release-cycle)
+[Patch Release Cadence](https://kubernetes.io/releases/patch-releases/#cadence)
+
+## Validation / Conformance
+
+*This section will be updated when the conformance tests are written.*