migrations-k8s-postgresql-upgrade: Major Postgres version upgrade playbook

Add a playbook to migrate the data on a Postgres PVC from a major version to another.

Invoke as:

$ ansible-playbook \
   -e k8s_context=do-ams3-k8s-apertis \
   -e namespace=qa-report-app \
   -e postgres_upgrade=14-to-15 \
   -e pg_pvc_data=data-postgresql-0 \
   -e pg_statefulset=postgresql \
   migrations-k8s-postgresql-upgrade.yaml

The playbook scales down the StatefulSet to 0 and then migrates the data on the PersistentVolumeClaim.

Once done, redeploy your Postgres using the new chart version.

Task: T10024