Keep some form of deep canyon or abyss (snapshot 21w06a feedback)

After some testing in snapshot 21w06a, I think that some form of canyon should be kept in the deep ocean biome.

• I have the impression that the deep ocean biome seems a bit dull after the updates to other biomes and without the canyons
• These canyons can be an interesting easy to mid-level challenge (could be even better with improved/specific enchants or tools)