Generate CRDs references for KGO and KIC

[czeslavo]

Problem Statement

Now that we have KIC and KGO CRDs living in this repository, we’ll need to find a way to generate sensible documentation from the API definitions we keep here (possibly separating KGO-supported and KIC-supported types so they can still be used in KGO and KIC CRD references).

Proposed Solution

So far we’ve been generating the markdown files for KIC and KGO CRDs using github.com/elastic/crd-ref-docs. The idea I have is to use the same tool, but annotate the CR types with markers telling whether the CRD is supported by KIC/KGO or both (e.g. // +kicsupported, // +kgosupported on a CR type level). We can inspect the markers (it's a native feature of crd-ref-docs) in templates and render docs only for types that a given project supports. Templates will still live in KGO and KIC repositories.

Additional Information

Acceptance Criteria

• KGO's CRDs markdown reference is rendered from kubernetes-configuration API definitions
• KIC's CRDs markdown reference is rendered from kubernetes-configuration API definitions

[czeslavo]

Removing a KGO 1.4 milestone as it's been done for KGO already while for KIC it will make more sense to be done together with Kong/kubernetes-ingress-controller#6488.

[randmonkey]

Looks like we should also allow KIC 3.4 milestone to refer to issues in the repo.

[pmalek]

Created https://github.com/Kong/kubernetes-configuration/milestone/3 and assigned it to this issue.