Add runtime CRD validation for database-type-specific fields in controller

[Copilot]

Description

Database CRD configs were not validated at the controller level, allowing Redis-specific fields (e.g. mode, rdb_path, invoke_save) to be set on non-Redis databases, and invalid mode values to be accepted for Redis.

Changes

• internal/controller/database_validator.go — new file with two functions:
  • validateDatabaseConfig(dbType, config): enforces that Redis mode is copy or sync if set, and that Redis-only fields are not present on non-Redis database types
  • validateDatabaseRefs(ctx, backup): fetches each referenced Database CRD via the dynamic client and runs validateDatabaseConfig against its config
• internal/controller/backup_controller.go — calls validateDatabaseRefs in both handleBackupCreate and handleBackupUpdate, after validateBackupSpec and before secret creation

Example: rejected configurations

# postgresql with a Redis-only field — rejected
type: postgresql
config:
  mode: copy       # ❌ field 'mode' is only valid for Redis databases, not for 'postgresql'

# redis with an invalid mode — rejected
type: redis
config:
  mode: dump       # ❌ redis 'mode' must be 'copy' or 'sync', got 'dump'

• internal/controller/database_validator_test.go — 25 unit tests covering valid and invalid configs for all supported database types

Related Issues

Checklist

• Your go code is formatted. Your IDE should do it automatically for you.
• New configuration options are reflected in CRD validation, helm charts and sample manifests.
• New functionality is covered by unit and/or e2e tests.
• You have checked existing open PRs for possible overlay and referenced them.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add crd validations in controller</issue_title>
<issue_description>In crds (e.g. database) some fields most be validated. For example for Redis mode field one of sync or copy is valid that should be checked in the controller. Or checking not to set mode for Postgresql which is a Redis field. etc.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add crd validations in controller #53

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