feat(clickhouse): make operator configs customizable

[abhinavmathur-atlan]

Summary

• allow replacing all five ClickHouse Operator configuration file maps through values
• preserve byte-identical default rendering when overrides are unset
• render each custom file before YAML serialization and reject non-string values clearly
• handle clickhouseOperator.configs: null safely
• add focused Helm unittest coverage

Testing

• helm lint charts/clickhouse
• full default render compared byte-for-byte with origin/main
• full custom render with all five ConfigMaps parsed and checked for exact round-trip values
• null-config render succeeds
• structured/non-string input fails with the expected validation error
• independent adversarial Claude review: APPROVE

Authored with Codex and independently adversarially reviewed with Claude.

Fixes #575