feat(groups): implement project grouping functionality

This commit introduces a new feature allowing users to organize projects into groups, enhancing project management capabilities.

Changes include:
- Addition of a "Groups" section in the UI for group creation, selection, and deletion.
- Methods for loading, rendering, and updating groups in the application.
- Project entities now support a `group` attribute, defaulting to 'Uncategorized' if not specified.
- Backend enhancements to handle group-related requests, including APIs for fetching, creating, renaming, and deleting groups.

These changes aim to improve user experience by providing better organization of projects, making it easier to manage and locate related tasks or items.

Author: Frederik Wystup