R66 server passwords are not decrypted in export files

Local R66 agents have a "serverPassword" field in their proto config, for authentication purposes. For security reasons, these passwords are encrypted using AES when inserted in the database.

However, the "waarp-gatewayd export" command does not decrypt theses passwords (like it does for other kinds of passwords) when writing the export file. As a result, these export files are unusable if re-imported in a Gateway instance which uses a different AES passphrase.

This should be fixed so that R66 server passwords are exported in plain text, like all other (non-hashed) passwords.