Move code from eventing-controller to eventing-manager

[friedrichwilken]

Description

Instead of importing the eventing-controller, move the relevant code over to the eventing-manager repository. Adjust accordingly.

• Eventing-controller code remains in the Kyma repository
• No modification on the event-publisher-proxy is to be done within this ticket

Pair on this ticket, to enable fast reviews.

For smoothest work: any work on the eventing-manager repository will be stopped, once this ticket is in progress. People who are not working on this issue, shall be working on the UI issue.

Acceptance Criteria ✅

• Eventing manager should not have any dependencies on the eventing-controller
• The move is split up in many small PRs

[mfaizanse]

• https://kubebuilder.io/migration/multi-group.html

[mfaizanse]

Following is the final PR to remove the eventing-controller dependency from eventing-manager:

• Moved api pkg from eventing-controller #260

Changes already done in this PR are:

• Renamed api/operator.kyma-project.io to api/operator and fixed imports.
• Renamed internal/operator.kyma-project.io to internal/operator and fixed imports.
• Copied eventing-controller/api/v1alpha1 to eventing-manager/api/eventing/v1alpha1
• Copied eventing-controller/api/v1alpha2 to eventing-manager/api/eventing/v1alpha2.
• Moved internal/subscription to internal/eventing/subscription.
• Removed eventing-controller from go.mod.
• Changed all eventing-controller imports to use eventing-manager.
• Deleted Subscription CRD from config/crd/external, because local CRD in created in config/crd/bases dir.

Things to do:

• Fix test in equality_test.go
• Test the PR on k8s cluster with NATS+EventMesh and Subscription v1alpha1+v1alpha2 CRs.
• Test upgrade from latest eventing-manager release to current PR.
  • Test conversion and validation webhooks for Subscription CRs.