fix: remote services ls always return a list

[lidel]

Closes #7824 cc @Gozala needed for 0.8.0 (#7707)

This PR ensures ipfs pin remote service ls --enc=jsonreturns a valid JSON with an empty list, even when Pinning.RemoteServices is missing from the config (eg. right after ipfs init, before any services are added/removed)

$ ipfs pin remote service ls --stat --enc=json
{"RemoteServices":[]}