refactor!: Replace product-config validation/serialization with typed builders

Reshape ValidatedCluster (name, image, cluster_config, role_group_configs) and
validate via framework::role_utils::with_validated_config. Build hive-site.xml,
security.properties and core-site.xml via dedicated builders + the vendored
writer. Switch HiveConfigOverrides to v2 KeyValueConfigOverrides (key-by-key
Merge). product-config is now only referenced by the crd Configuration impl.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: maltesander