cli: manage gives no warning for the secret flags of its subcommands #916

#849 makes extenddb manage print a warning on stderr when the password comes from --password. Four subcommand flags carry secrets with the same exposure in process listings and shell history. They get no warning, and no environment variable can replace them (crates/app/src/manage_types.rs on main at 35edb77):

• --admin-password on create-admin: the password of the new admin.
• --new-password on change-admin-password and change-user-password: the new password.
• --user-password on create-user: the console password of the new IAM user.
• --secret-access-key on import-access-key: the imported secret key.

For example, manage --password X create-admin --admin-password Y warns about X and says nothing about Y. The S-2 row of docs/technical-debt.md records the gap, and this issue tracks it.

Raised in the review of #849.