cmd/clef: encrypt the master seed on disk (#17704)

* cmd/clef: encrypt master seed of clef

Signed-off-by: YaoZengzeng <yaozengzeng@zju.edu.cn>

* keystore: refactor for external use of encryption

* clef: utilize keystore encryption, check flags correctly

* clef: validate master password

* clef: add json wrapping around encrypted master seed