workaround for .Capabilities.APIVersions

[kd7lxl]

What this PR does:
#227 introduced policy/v1 for PodDisruptionBudgets with a conditional based on .Capabilities.APIVersions:

cortex-helm-chart/templates/compactor/compactor-poddisruptionbudget.yaml

Line 2 in ad6ebfd

{{- if .Capabilities.APIVersions.Has "policy/v1"}}

By default, helm template populates .Capabilities.APIVersions with all API versions known to Kubernetes client-go v1.22. Many CD tools use this to render the template, then naively try to deploy to Kubernetes clusters that don't support policy/v1, such as v1.20 (e.g., argoproj/argo-cd#7291). This results in error messages like no matches for kind "PodDisruptionBudget" in version "policy/v1".

helm template provides a couple ways to hint a more specific set of API versions:

• --api-versions can explicitly append API versions to .Capabilities.APIVersions
• --kube-version can override .Capabilities.KubeVersion, but doesn't have any effect on .Capabilities.APIVersions
• --validate will interrogate Kubernetes to get an accurate list of API versions

Currently, this chart only works currently with helm template --validate and helm install.

This PR provides a workaround so that all three methods of hinting API version support to helm template work as expected. This should make it easier for users of naive CD tools to deploy this chart successfully.

Demo with various options:

% helm template . -s templates/distributor/distributor-poddisruptionbudget.yaml | grep apiVersion
apiVersion: policy/v1beta1
% helm template . -s templates/distributor/distributor-poddisruptionbudget.yaml --kube-version v1.20 | grep apiVersion
apiVersion: policy/v1beta1
% helm template . -s templates/distributor/distributor-poddisruptionbudget.yaml --kube-version v1.21 | grep apiVersion 
apiVersion: policy/v1
% helm template . -s templates/distributor/distributor-poddisruptionbudget.yaml --api-versions=policy/v1/PodDisruptionBudget | grep apiVersion
apiVersion: policy/v1
% helm template . -s templates/distributor/distributor-poddisruptionbudget.yaml --validate | grep apiVersion
apiVersion: policy/v1

Checklist

• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[nschad]

Tested with ArgoCD, works great!

[nschad]

Improvement: #279