Improper permission checks in Jenkins Swarm Plugin

Swarm Plugin adds API endpoints to add or remove agent labels. In Swarm Plugin 3.20 and earlier these only require a global Swarm secret to use, and no regular permission check is performed. This allows users with Agent/Create permission to add or remove labels of any agent.

Swarm Plugin 3.21 requires Agent/Configure permission for the affected agent to these endpoints. It no longer uses the global Swarm secret for these API endpoints.