🌱 update fleetconfig API to support configuring add-ons

[arturshadnik]

Proposal

Fleetconfig Controller can support creating and installing arbitrary ManagedClusterAddOns by leveraging the clusteradm addon command.

Changes

This PR proposes the API changes for supporting add-ons. The following changes are added.

FleetConfig.Spec.AddOns

• Add-ons to be configured on the hub and become available to install onto spokes
• Exposes all the flags of the clusteradm addon create command
• The manifests to be used for creating the addons are provided via the helm chart and can be in one of 2 formats:
  1. inline manifests
  2. URL to download the manifests. A URL pointing to a .yaml file can be used directly, and OCI artifacts would be downloaded first and written to a temp file.
• The manifests for all the AddOns will be saved to a single configmap, where each key corresponds to FleetConfig.Spec.AddOns[*].Name, and the value will be either the URL or the raw manifests to be consumed by the controller

FleetConfig.Spec.Spokes[*].AddOns

• The add-ons to enable for that specific spoke.
• Supports configuring an installNamespace and adding annotations, in line with what the clusteradm addon enable command supports
• FleetConfig.Spec.Spokes[*].AddOns[*].Name corresponds to one of the top-level add-ons, or a default add-on (TBD in a followup)

TODO

This PR does not introduce any changes to the controller code. The following work will be done in followup PRs:

1. Controller implementation
   a. Handling the full lifecycle of the AddOnTemplates and other Hub resources
   b. Handling the full lifecycle of ManagedClusterAddOns as spoke clusters are joined and unjoined
2. Configuring default add-ons in the FleetConfig Controller helm chart that will be created and reconciled in all cases.

[openshift-ci]

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This pull-request has been approved by: arturshadnik

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[ahmad-ibra]

/lgtm