What is the purpose of this change?

Propose a backend implementation for Infomaniak's kDrive storage

A new "kdrive" backend is added. The code was initially copied from the "pcloud" backend, and then modified to match the kDrive API.

Was the change discussed in an issue or in the forum before?

A request for this backend appeared some time ago, here: #8456

This is my first contribution to rclone, and my first attempt at the Go language, so while I'm trying to follow the good practices, be aware there might be many mistakes in this new backend... This is still a WIP, and this PR is intended to start the convergence on the code of the backend.

The documentation for the backend is still missing; I'll add it soon.

Checklist

• I have read the contribution guidelines.
• I have added tests for all changes in this PR if appropriate.
• I have added documentation for the changes if appropriate.
• All commit messages are in house style.
• I'm done, this Pull Request is ready for review :-)