refactor(core): change scaffolding to use kubebuilder v4 structure

[IvoGoman]

Description

This updates the structure of the repository to more closely follow the kubebuilder/v4 scaffolding.
The previous structure was not following any kubebuilder scaffolding, thus made it hard to generate new apis/controllers/webhooks.

This also changes how CRDs are generated. In order to make patching the CRDs easier the makefile now builds the CRDs with kustomize and then copies them into the helm chart.

TODO:

• sort out the /config folder, this currently contains all auto generated kustomize files
• revisit hack/helmify.sh and potentially replace this with kustomize patches
• make sure current consumers are updated (kubeconfig-generator, repo-guard)
• double-check scaffolding now works seamlessly
• update getting-started docs

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

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

[kengou]

We need this 2 files for infra automation
config/manifest/flux-installation-main.yaml
config/manifest/flux-installation-release.yaml

[kengou]

lgtm

[abhijith-darshan]

could we remove the sub-folder greenhouse in the api section?

Instead of

api
|_greenhouse
   |_v1alpha1
   |_v1alpha2
   |_well-known
   |_docs

Let's keep

api
 |_v1alpha1
 |_v1alpha2
 |_well-known
 |_docs 

We would need to update the import paths everywhere, which I addressed in - https://github.com/cloudoperators/greenhouse/tree/feat/enable-conversion-webhooks