remove erronous dependency on cloudbees-credentials

[jtnord]

the plugin erroneously depended on cloudbees-credentials which is a deprecated plugin that is used to provide credentials to access CloudBees services.

remove the dependency requirement so that people can remove the unused dependency

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

@r2liquibase

[cniweb]

@jtnord or @bmunozm When does this continue? We urgently need the update!
Background: Deprecated CloudBees Enterprise Plugins, see:
https://docs.cloudbees.com/docs/cloudbees-ci-kb/latest/client-and-managed-masters/uninstall-deprecated-cloudbees-enterprise-plugins

[cniweb]

@prospero238 or @r2liquibase When does this continue? We need the update urgently too!