[FEAT] - Deletion Protection for PluginPresets

[IvoGoman]

Priority

(Medium) I'm annoyed but I'll live

User Story

As an Org Admin I would like to have additional protection on the PluginPreset resources, so that they cannot be easily deleted by accident.

Description

The PluginPreset can create Plugins for a multitude of clusters. When the PluginPreset is deleted, also all of these Plugins are removed. This can break/ remove a lot of Helm Releases.
In order to protect from this, the PluginPreset's should get an additional annotation that prevents a deletion to succeed. (greenhouse.sap/prevent-deletion).
The webhook needs to ensure that deletion requests for PluginPresets with this annotation are rejected with an appropriate error message.
This annotation should be set on every PluginPreset, whenever it is created.

Acceptance Criteria

• Webhook ensures greenhouse.sap/prevent-deletion during PluginPreset Create admission
• Webhook ensures deletion is blocked in case the annotation is set
• Documentation of PluginPreset contains a section on how to delete a PluginPreset
• Tests to verify the added behavior

Reference Issues

No response