[greenhouse-mgmt] Create PluginConfig plugin

[edda]

Create a "PluginAdmin" plugin for the greenhouse management area which will show installed/configured plugins and available (not yet installed/configured) plugins. Eventually this plugin will also allow de-/activation and configuration of plugins.

First steps:

• [x] Create a new ui plugin in greenhouse/ui (as an external Juno app)
• [x] Ensure the new plugin is built by a pipeline
• [x] Add plugin to greenhouse-management side navigation
• [x] plugin needs auth and k8sclient

Plugin first steps:

• [x] use k8sclient to load all available pluginconfig resources and render a list of them
• [x] for each pluginconfig items in list add a details view (opens in Panel) which at first displays the pluginconfig in a JSONView (see Supernova AlertDetails as inspiration)
• [x] Check which metadata makes sense to extract specifically from the JSON to display in the list view and in the details view in a key/value type section (similar to Supernova AlertDetails)

[ArtieReus]

This is the way how to retrieve the exposedServices from the plugin configs:

kc greenhouse-qa
kn ccloud
k get pluginconfig kube-moni-ext -o json

{
    "apiVersion": "greenhouse.sap/v1alpha1",
    "kind": "PluginConfig",
    ...
    "status": {
        "description": "Native deployment and management of Prometheus along with Kubernetes cluster monitoring components.",
        "exposedServices": {
            "https://kube-moni-ext-prometheus--ccloud--monitoring.ccloud.greenhouse-qa.eu-nl-1.cloud.sap": {
                "name": "kube-moni-ext-prometheus",
                "namespace": "ccloud",
                "port": 9090
            }
        },
        ...
    }
}