Run a link checker on every PR

[porridge]

What would you like to be added:

We should check at least internal links to make sure there are no 404s.

Why is this needed:

Example: #228

[d2iq-shadowbq]

Possible use pre-commit (as already used in Kudo) with a configuration to use:

One of the following:

• vuepress-plugin-check-md (https://github.com/ulivz/vuepress-plugin-check-md)
• the npm based blc (https://github.com/stevenvachon/broken-link-checker)

[d2iq-shadowbq]

Reference: #100

[d2iq-shadowbq]

$ vuepress check-md content

Checking markdown...

21 dead links was found

  File is not found: [test harness](../docs/testing) (/app/content/blog/announcing-kudo-0.3.0.md:64:143)
  Hash is not found: [Learn Custom Resource Definitions](#learn-custom-resource-defintions) (/app/content/blog/blog-2019-12-06-mesos-to-kudo.md:33:4)
  Hash is not found: [Dynamic CRD / KUDO](#dynamic-crd-kudo) (/app/content/blog/blog-2019-12-06-mesos-to-kudo.md:35:4)
  File is not found: [operator repository](repository.md) (/app/content/docs/architecture.md:28:177)
  File is not found: [^CRD]: [Custom Resources](https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/) (/app/content/docs/comparison.md:86:1)
  File is not found: [^RBAC]: [Using RBAC Authorization](https://kubernetes.io/docs/reference/access-authn-authz/rbac/) (/app/content/docs/comparison.md:87:1)
  File is not found: [^finalizers]: [Using Finalizers](https://book.kubebuilder.io/reference/using-finalizers.html) (/app/content/docs/comparison.md:88:1)
  File is not found: [^charts]: [Helm Charts](https://github.com/helm/charts) (/app/content/docs/comparison.md:89:1)
  File is not found: [^kustomization]: [kustomize workflows](https://github.com/kubernetes-sigs/kustomize/blob/master/docs/workflows.md) (/app/content/docs/comparison.md:90:1)
  File is not found: [^cnab]: [CNAB Specification](https://github.com/deislabs/cnab-spec) (/app/content/docs/comparison.md:91:1)
  File is not found: [execute a plan](what-is-kudo.md#operator-parameters) (/app/content/docs/developing-operators/plans.md:146:45)
  Hash is not found: ["configuration" section in the "managing" page](./managing.md#configuration) (/app/content/docs/runbooks/cassandra/installing.md:158:1)
  File is not found: [operating](./operating.md) (/app/content/docs/runbooks/cassandra/installing.md:160:1)
  File is not found: [the monitoring directory](../monitoring/grafana) (/app/content/docs/runbooks/cassandra/monitoring.md:74:1)
  File is not found: [labels on the `ServiceMonitor` resource](../operator/templates/service-monitor.yaml#L7) (/app/content/docs/runbooks/cassandra/monitoring.md:92:1)
  Hash is not found: [KUDO controller/manager logs](#kudo-controllermanager-logs) (/app/content/docs/runbooks/cassandra/managing.md:14:5)
  File is not found: [params.yaml](../../operator/params.yaml) (/app/content/docs/runbooks/spark/configuration.md:12:79)
  File is not found: [spark-operator-rbac.yaml](../../operator/templates/spark-operator-rbac.yaml) (/app/content/docs/runbooks/spark/configuration.md:68:86)
  File is not found: [spark-rbac.yaml](../../operator/templates/spark-rbac.yaml) (/app/content/docs/runbooks/spark/configuration.md:76:14)
  File is not found: [params.yaml](../../operator/params.yaml) (/app/content/docs/runbooks/spark/monitoring.md:27:87)
  File is not found: [KUDO](kudo.dev) (/app/content/docs/runbooks/kafka/concepts.md:3:53)

[porridge]

This ☝️ seems to have quite a few false positives, e.g. File is not found: [^charts]: [Helm Charts](https://github.com/helm/charts) (/app/content/docs/comparison.md:89:1) is clearly wrong.

Oh, I get it, it does not understand the [^...] footnote syntax.

[d2iq-shadowbq]

lets move the recommendation discussion on the plugin to the PR.

[porridge]

Reopening, since the goal of this ticket was to provide feedback to PR author that there are broken links.
As #281 shows, what was currently done is not nearly enough - all checks (but the dreaded DCO) are green.