Rename any attestation wording from sidecar

[gjermundgaraba]

Since the sidecar is not really attesting (signing) to anything anymore, it is primarily a tool for the validators to query ibc data. Therefore, any wording of attestation, attestor or anything like that should be renamed in the sidecar.

It can still be called the attestation-sidecar (since it is a sidecar process for the attestation process).