Enable flows in projects and groups

Summary

The MR to use flows in a project or group has landed: !198628 (merged). Task of this issue is to add the UI to use a flow in a project or group.

Scope

• For testing and demo showcases, consider adding a simple input field for the project ID or group ID combined with a type selector (for 'project' or 'group') similar as we do it for the project ID when creating and agent.
• Afterwards, create an issue to use better UI components, such as dropdown selectors, which are prefilled with group and project data which was fetched from the Backend. These dropdown selectors should only show objects to which the user has access for.

Out of scope

• There is another issue (!198628 (merged)) to remove the usage again. It is not part of this issue.
• There is another issue (#557559) to show usage numbers on lists. It is not part of this issue