[DSIP-105][Feature][API] Encrypt sensitive definition params with PasswordUtils

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Description

Subtask of #17937 (DSIP-105). Depends on #18586 (Property.sensitive + API/UI masking).

Reuse existing PasswordUtils.encodePassword / decodePassword for definition-time at-rest protection of sensitive=true values. Do not change datasource CRUD.

In scope

• On workflow/task definition save: encode new plaintext sensitive values when datasource.encryption.enable=true
• Keep-original (******) writes the DB value as-is; never re-encode
• Empty / null is a real empty value (PasswordUtils empty → ""), not keep-original; ****** is write-path only and is never decoded
• false → true: on create, reject ****** (no existing value to merge); on update, ****** is keep-original — merge the existing plaintext, then encode and persist with sensitive=true
• true → false: decode then persist plaintext with sensitive=false
• Internal execution / start merge uses a decrypt copy; API/UI still return masked copies only
• Runtime instance global_params stays plaintext materialization (as agreed on the parent)
• Same-cluster Copy copies JSON as-is (ciphertext + sensitive); no double encryption

Out of scope

• Datasource create/update/password UI (reuse utils only)
• Worker log masking (see Worker subtask)
• Project parameters, Export / Import, KMS / key rotation
• Encrypting instance global_params

Acceptance

• With encryption on, sensitive definition values are not stored as plaintext in DB JSON
• Saving unchanged sensitive params (******) does not double-encrypt
• After Copy, sensitive params still work at runtime
• API/UI still return ****** (decrypt is internal-only)
• Encryption off (default): behavior matches #18586 except encode is skipped
• Unit tests: encode new plaintext only; keep-original; false↔true; encryption flag on/off

Use case

Definition JSON in the metadata DB should not store secrets in plaintext when the existing datasource encryption switch is enabled. Runtime still materializes plaintext for dispatch.

Related issues

• Parent DSIP: #17937
• Depends on: #18586

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct