To match the registry server refactoring changes introduced in 70b40d3946
No data was changed apart from promoting the fields.
The changes produced by this commit can be reproduced with:
$ jq -c 'with_entries(.value.version=.value.contract.version | .value.issuer_pubkey=.value.contract.issuer_pubkey)' index.json | sponge index.json
$ ls ??/*.json | while read file; do jq -c '.version=.contract.version | .issuer_pubkey=.contract.issuer_pubkey' $file | sponge $file; done
