routing get|put: restore old JSON wire format

[lidel]

Changes from ipfs/specs#351 are causing issues in bifrost-gateway, we need to restore JSON format from https://docs.ipfs.tech/reference/kubo/rpc/#api-v0-routing-get and https://docs.ipfs.tech/reference/kubo/rpc/#api-v0-routing-put before we ship Kubo 0.19.