Support various equipment layouts in racks as plugins

[rezib]

Currently, racksdb support only one layout for a set of equipments in InfrastructurePart, ie. the bottom-up Z as explained in the documentation : https://docs.rackslab.io/racksdb/beta/db/positioning-equipments.html

While it seems a fair default layout, it should support additional programable layout with plugins. The InfrastructureDrawer should then call the layout plugin to define the top left corner of an equipment.