Document the JWT removal

https://redmine.teklia.com/issues/10050

Requires enterprise#50

• Remove the jwt_signing_key setting

• Mention in the upgrade notes that the authentication system for Ponos agents in EE only has changed:

  • All agents must upgrade to Ponos version insert next release here or above
  • The previous versions are borked!

changed milestone to %Arkindex 1.7.3

added P2 label

assigned to @erouchet

changed the description

mentioned in merge request !219 (merged)

closed with merge request !219 (merged)