Document the ability to add addons

[nwneisen]

The MKE4 config allows for users to add components outside of what is provided as part of MKE4. This is done by using the addon section in the config. The metallb section is one of these that we provide but users can do the same with any helm charts or manifests that they want.

  addons:
  - chart:
      name: metallb
      repo: https://metallb.github.io/metallb
      values: |
        controller:
            tolerations:
                - key: node-role.kubernetes.io/master
                  operator: Exists
                  effect: NoSchedule
        speaker:
            frr:
                enabled: false
      version: 0.14.7
    dryRun: false
    enabled: true
    kind: chart
    name: metallb
    namespace: metallb-system

This addon section will basically pass the values through to BOP and follows the same format as a blueprint:
https://mirantiscontainers.github.io/blueprint/docs/blueprint-reference/components/

[KoryKessel-Mirantis]

@nwneisen, do you envision this content under Concepts or Getting Started (I can see it in either)?

[nwneisen]

I could see detailed information being under concepts and adding a basic "hello world" addon part of the getting started