Support for Jottacloud as a Backend.

### Please agree to the following

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

### Summary

Please add support for using Jottacloud as a storage backend.

### Motivation

Jottacloud is a Norwegian cloud provider with around million users.

A rclone backend already exists, which can be used for basing the backend on.

### Considered Alternatives

_No response_

### Anything else?

_No response_

Start by reviewing the repository’s existing storage-backend implementations and the Jottacloud backend in rclone, since no project files or tests are named. Done means Jottacloud can be used as a storage backend and the relevant existing tests pass.

Written by the indexing model from the issue text.