Rename database password toggle

* otherwise submitting the form with the password show will be overwritten
* see https://github.com/nextcloud/server/blob/2c9d7eeb763d2f907eea8234f6c60a829a5d39f7/core/Controller/SetupController.php#L59


* seems to be a legacy fallback
* fixes #3381

Signed-off-by: Morris Jobke <hey@morrisjobke.de>