Migrate to Kubebuilder v3

[zroubalik]

Signed-off-by: Zbynek Roubalik zroubali@redhat.com

I have migrated the project to Kubebuilder v3 (https://book.kubebuilder.io/migration/migration_guide_v2tov3.html)
Most of the changes are just moving files/packages etc. No big changes related to functionality.

• API path has changed to include keda group, so we are more aligned with the way how client-go expects it: github.com/kedacore/keda/v2/api/v1alpha1 -> github.com/kedacore/keda/v2/apis/keda/v1alpha1
• controllers has been moved the similar way API was: controllers/ -> controllers/keda/
• bump controller-runtime to v0.10.0
• bump k8s deps to v0.22.1
• bump other deps
• there were a few other minor code changes
• I have added license header to majority of files

Checklist

• Commits are signed with Developer Certificate of Origin (DCO - learn more)
• A PR is opened to update our Helm chart (Reflect changes with migration to Kubebuilder v3 charts#184)
• Changelog has been updated