* encrypt migration credentials in task persistence
Not sure this is the best approach, we could encrypt the entire
`PayloadContent` instead. Also instead of clearing individual fields in
payload content, we could just delete the task once it has
(successfully) finished..?
* remove credentials of past migrations
* only run DB migration for completed tasks
* fix binding
* add omitempty
* never serialize unencrypted credentials
* fix import order
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
