feat(pluginpresets): specify and propagate plugin dependencies via waitFor

[Zaggy21]

Description

This PR adds a list of PluginRefs into .spec.waitFor in PluginPresets and Plugins. Plugin dependencies are verified on the HelmRelease level. Webhooks validate that each PluginRef has only one value set: Name or PluginPreset. PluginPresetController copies over all PluginRefs in PluginPresets to Plugin's waitFor. Then Flux PluginController resolves the dependencies by transforming PluginRefs so that only Plugin names are set and sets them on spec.dependsOn in the HelmRelease for the Plugin (because plugin name equals helm release name).
This PR also introduces a new status condition on Plugins: WaitingForDependencies condition. The message about not ready dependencies is propagated from flux into the condition.

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] - PluginPreset & Plugin specify .spec.waitFor #1420
• Closes [FEAT] - Propagate .spec.waitFor from PluginPreset to Plugin #1422
• Closes [FEAT] - Plugin status reflects missing depedencies #1524

Added tests?

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

Added E2E test that checks that WaitFor is propagated and the Flux waits for dependent HelmRelease to be installed first.

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