ui-spacetimechart: add occupancy blocks layer

[Akctarus]

closes https://github.com/OpenRailAssociation/osrd/issues/9158

[emersion]

"Bloc" seems… very French :P

Should it be "block"? Or is there a better English translation for "bloc d'occupation"?

Edit: reading the docs, seems like "block" is the right word to use here.

[emersion]

I'd also recommend not doing the same mistake I did :P https://github.com/OpenRailAssociation/osrd-ui/pull/624

[emersion]

Do we have a mockup for this?

[Akctarus]

Do we have a mockup for this?

Yes :

and : https://www.sketch.com/s/bcbac4ff-7f74-4f1a-9e10-08d115c47ed8/p/C0FA571F-D55C-40A1-B0E0-B61D135726CD/canvas