Add more information on hover pixel map

[berombau]

One of the main benefits of using napari to view the phenotype maps is the ability to add extra information. One usecase is showing the cluster names when hovering over the map in napari-spatialdata, not just the cluster index in the color map of the Labels layer.

Possible with custom mouse functions: https://github.com/napari/napari/blob/main/examples/custom_mouse_functions.py
Similar to: napari/napari#531

Possible future support for more bespoke tooltip in napari, but implemented in the plugin: napari/napari#6570