Add Chunk load/unload events

[bziemons]

Currently, there are load/save events for chunk data in dev.architectury.event.events.common.ChunkEvent, but I am missing chunk loading/unloading lifecycle events.
I am developing for 1.20.1 (that is the current target for playability with other mods/modpacks). Assuming this is something that is warranted in the Architectury API: how would I go about adding these events in a pull request? First of all, what branch would I target? And what else would I need to take care of? Is there a document describing this process?
I have seen PR #464 which adds another chunk event, but the event is afaict not available in the newest Architectury API on 1.21, so I cannot deduce the actual process from this PR.

In Fabric's API, the events I need are defined in net.fabricmc.fabric.api.client.event.lifecycle.v1.ServerChunkEvents and in (Neo)Forge they would be in net.minecraftforge.event.level.ChunkEvent.