Update user membership on login

### Please agree to the following

- [X] I have searched [existing issues](https://github.com/cryptomator/hub/issues?q=) for duplicates
- [X] I agree to follow this project's [Code of Conduct](https://github.com/cryptomator/hub/blob/develop/.github/CODE_OF_CONDUCT.md)

### Summary

Update user membership on login

### Motivation

Users and groups are synced in regular intervals with Keycloak. If a user is removed within this interval from the group, in Hub they are still part of the group.

To mitigate such security relevant issues, the user group membership should be synced on every login.

### Considered Alternatives

_No response_

### Anything else?

The problem currently is, that the claim of the Keycloak group mapper can only contain the path and or name of the group, not the ID. Updating group memberships based on the path isn't a good idea. We need to wait until group IDs can be added to the claim.