feat: use a signing secret instead of a deprecated verification token (#104)

Description

Use a signing secret instead of a deprecated verification token

Examples

Run Joe with the key --signing-token instead of the --verification-token

Related issue

#104 (closed)

Checklist

• the MR description has been reviewed
• this MR contains text changes and they have been reviewed OR there are no texts changes
• this MR contains GUI/CLI changes and they have been reviewed OR there are no GUI/CLI changes
• this MR contains API changes and they have been reviewed OR there are no API changes

Closes #104 (closed)