Prepare for initv3 on bookworm

[ashthespy]

To avoid more diverging trees, have brought in all the good work from @gkkpch and @foonerd in foonerd/vos3-initv3 here.

What this aims for:

• [untested] Devices should be able to move b/w old and new init
• Plymouth themes are set at device level, but copied at image level 8c54d7aab011cc6e6b1c982793f18e5529f480e3

@foonerd Could you try building an image and see if the init portions behave as expected, will then merge this to dev/bookworm Note, this is just a base image, and will have most bookworm issues from #172.

x86 recipe will need some updates for bookworm, and will error out currently with missing paths for UCM.

[gkkpch]

To consider: instead of installing the plymouth-themes package, which unnecessarily increases the size of our initramfs, try whether only plymouth-label can be installed. We need the plymouth.label.so plugin but not the themes themselves.

[ashthespy]

Closing this, will let the dust settle in #179 and merge in bookworm tree :-)