Drop yaml support in cluster_dump

[hendrikmakait]

Our cluster_dump functionality is currently broken wrt. key roundtrips (#8540), which we need to fix. Since I do not see the added value in supporting both msgpack and yaml, I'm inclined to limit the fix for roundtripping to msgpack and drop support for yaml without a deprecation cycle. (It's mostly broken anyways.) Note that we will still have DumpArtefact.to_yamls in case users want to create human-readable files. Also, msgpack is already a required dependency.

[fjetter]

Actually, msgpack was added only later because the dumps grew too large. the benefit of yaml is that it is human readable. I often analyzed those dumps by grepping/searching and reading the files.
I'm fine with dropping support for the dump to be written directly to yaml but there is also DumpArtefact.to_yamls which probably has the same problem

[hendrikmakait]

I'm fine with dropping support for the dump to be written directly to yaml but there is also DumpArtefact.to_yamls which probably has the same problem

It will. Since we won't have to be able to roundtrip, I think we can get away with a simpler implementation here, i.e., simply stringifying keys. You could then grep for the stringified key in the yaml files.

[crusaderky]

+1. I like human-readable but converting from msgpack when needed is 3 lines

[hendrikmakait]

Closing this as not planned. In #8540, we decided against touching cluster dumps at all for now.