ci: update changelog (keptn#953)

BREAKING-CHANGE: The handling of the CRD lifecycle and metrics has been split into two different operators

feat(operator): adapt KeptnEvaluationDefinition to reflect changes in KeptnMetric and KeptnMetricsProvider
feat: use helmify to release our helm chart
feat(metrics-operator): added conversion webhook for KeptnMetric CRDs
feat(cert-manager): support certificate injection for all matching resources based on label selector
feat: introduce lifecycle.keptn.sh/v1alpha3 API version
feat(metrics-operator): allow KeptnMetrics to be placed in any namespace
feat: adapt examples to use KeptnMetric and KeptnMetricsProvider
chore(operator): remove KeptnMetric and KeptnEvaluationProvider from klt operator
fix(metrics-operator): adapt metric types from v1alpha1
fix(operator): invalid import of metrics
feat(metrics-operator): implement metric functionality
ci(metrics-operator): adapt pipelines
feat(metrics-operator): introduce migration from KeptnEvaluationProvider to KeptnMetricsProvider
feat(metrics-operator): introduce KeptnMetricsProvider CRD
feat: added the metrics-operator