⏲ Add initContainers to jobs to wait for dependencies instead of crashing (demos)

[!NOTE]
This came out of the 25.3.0 Release Retro

Many demos have (Job or other) pods showing CrashLoopBackoff until their dependencies are satisfied.

This causes confusion when launching demos, especially during demo testing.

Each stack/demo should make use of initContainers to wait for dependencies to be satisfied without giving false failure indications.

[!TIP]

• Ensure a ServiceAccount is created and attached to applicable Pods, and give it permissions to watch Jobs/Pods so it can wait.
• Ensure the ServiceAccount doesn't specify a namespace so that the demo can be installed into any namespace.
• Use namespace scoped RBAC (Role/RoleBinding instead of ClusterRole/ClusterRoleBinding).

List of demos

cat demos/demos-v2.yaml | yq -yr '.demos | keys' | sed 's/^-/- [ ]/'

• airflow-scheduled-job
• data-lakehouse-iceberg-trino-spark
• end-to-end-security
• hbase-hdfs-load-cycling-data
• jupyterhub-keycloak
• jupyterhub-pyspark-hdfs-anomaly-detection-taxi-data
• logging
• nifi-kafka-druid-earthquake-data
• nifi-kafka-druid-water-level-data
• signal-processing
• spark-k8s-anomaly-detection-taxi-data
• trino-iceberg
• trino-taxi-data

[!WARNING]
It is possible that some stacks also need the same treatment, but most of the waiting can be done in the actual demo.

Start with demos/demos-v2.yaml and review the listed demos, using the linked nifi-kafka-druid-water-level-data serviceaccount.yaml and setup-superset.yaml as the reference. Check each applicable demo's Kubernetes manifests for dependency waits, namespace-scoped RBAC, and attached ServiceAccounts. Done means applicable demo pods wait for dependencies instead of showing premature CrashLoopBackOff failures.