feat: Upgrade kratos client to 0.9.0-alpha3, add error handling for password

Closes #33 (closed)

To upgrade Kratos to version 0.9.0-alpha3 we need to make some changes. Most notably the identities endpoint moved to /admin/identities. I also upgraded the kratos python library to make sure the web/ stuff still works.

Apart from that, during testing, I noticed that errors were not rendered in the web/ part of the application. I added a page that renders Kratos errors (kratos is configured to use this page in stackspin!1012 (merged)). I also added rendering for messages about failed password upgrades.