Support /.well-known/change-password url for changing passwords

https://web.dev/change-password-url/

Set a redirect from `/.well-known/change-password` to the change password page of website. This will enable password managers to navigate your users directly to that page.

## Browser compatibility
A well-known URL for changing passwords has been supported in Safari since 2019. Chrome's password manager is starting to support it from version 86 onwards (which is scheduled for Stable release in late October 2020) and other Chromium-based browsers may follow. Firefox considers it worth implementing, but has not signalled that it plans to do so as of August 2020.