[EPIC] - Encourage PluginPresets as the only interface for Plugin creation

[uwe-mayer]

Description

Currently we have 2 similar entities:

• Plugins: a single deployed instance of a Greenhouse Plugin
• PluginPresets: A suite of Greenhouse Plugins with the same configuration deployed to a fleet of Clusters

This is confusing to the user and more difficult to maintain. Also clients (mainly UI) need to make distinctions on CREATE or UPDATE.

Objectives

• Encourage PluginPresets as the only interface for creating Plugins
  - Maintain Plugins only as technical resource with no client/user interaction

Acceptance Criteria

• PluginPresets allow selection of single Cluster
• PluginPresets show Status of dependent Plugins
• PluginPresets have an aggregated Status of dependent Plugins

- [ ] Decide on how to deal with `Plugins deployed to the central Cluster: AdminPlugins

- [ ] Client interaction with Plugins is denied

- [ ] Migrate all Plugins from the CCloud Organization into PluginPresets

[IvoGoman]

Closing the #829. We still need to be able to create Plugins for now and should probably keep the possibility open in the future as well. This does not interfere with the plan to support just the creation of new PluginPresets from the Greenhouse UI

[IvoGoman]

Plugins will stay as a way to create Plugins, the preferred way will be the PluginPreset. Dashboard will only support the PluginPreset, creating a single Plugin will stay possible via Kube API.