feat(pluginpresets): remove admission check on PluginDefinition existence

[IvoGoman]

Description

In order to make PluginPresets more CI-friendly. The admission check for (Cluster-)PluginDefinition existence has been removed.

If the PluginPreset references a non-existing (Cluster-)PluginDefinition this will be reflected in the Status on the next reconciliation.

Co-authored-by: Copilot copilot@github.com

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation Update
• 🎨 Style
• 🧑‍💻 Code Refactor
• 🔥 Performance Improvements
• ✅ Test
• 🤖 Build
• 🔁 CI
• 📦 Chore (Release)
• ⏩ Revert

Related Tickets & Documents

• Closes [FEAT] - Move existence check of (Cluster-)PluginDefinition for PluginPreset to reconciliation #1848

Added tests?

• 👍 yes
• 🙅 no, because they aren't needed
• 🙋 no, because I need help
• Separate ticket for tests # (issue/pr)

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Added to documentation?

• 📜 README.md
• 🤝 Documentation pages updated
• 🙅 no documentation needed
• (if applicable) generated OpenAPI docs for CRD changes

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

[Copilot]

Pull request overview

This PR makes PluginPresets “CI-friendly” by removing the admission-time requirement that the referenced (Cluster-)PluginDefinition already exists, and instead surfaces missing definitions via PluginPreset status during reconciliation.

Changes:

• Updated PluginPreset validating webhook to stop fetching/validating referenced (Cluster-)PluginDefinition on create.
• Added controller logic + test to reflect missing PluginDefinition via PluginFailed condition (reason PluginDefinitionNotFound) and propagate message into Ready condition.
• Updated docs to describe the new behavior and removed outdated “immutable” wording for Plugin’s pluginDefinitionRef.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/webhook/v1alpha1/pluginpreset_webhook.go	Removes admission-time (Cluster-)PluginDefinition existence/option validation for PluginPreset create.
internal/webhook/v1alpha1/pluginpreset_webhook_test.go	Adjusts admission tests to expect PluginPreset creation to succeed even when definitions are missing.
internal/controller/plugin/pluginpreset_controller.go	Attempts to detect missing PluginDefinition during plugin reconciliation and set PluginFailed/Ready messaging accordingly.
internal/controller/plugin/pluginpreset_controller_test.go	Adds coverage asserting PluginPreset status reflects a missing (Cluster-)PluginDefinition.
api/v1alpha1/pluginpreset_types.go	Introduces PluginDefinitionNotFound condition reason constant.
docs/user-guides/plugin/plugin-management.md	Documents new “admit first, reflect missing definition in status” behavior.
docs/reference/components/pluginpreset.md	Adds note that PluginPreset may reference a not-yet-created PluginDefinition.
docs/reference/components/plugin.md	Removes “immutable” wording for spec.pluginDefinitionRef.

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