Use Spring security API instead of Acegi security

[Vlatombe]

Use Spring security API instead of Acegi security

• Downstream usage of [JEP-227][JENKINS-39324] Replace Acegi Security with Spring Security APIs credentials-plugin#490

Checklist

• I have read the CONTRIBUTING doc
• Unit tests pass locally with my changes
• I have added documentation as necessary
• No Javadoc warnings were introduced with my changes
• No spotbugs warnings were introduced with my changes
• Documentation in README has been updated as necessary
• Online help has been added and reviewed for any new or modified fields
• I have interactively tested my changes
• Any dependent changes have been merged and published in upstream modules (like git-client-plugin)

Types of changes

• Use modern API instead of the deprecated API

[MarkEWaite]

Thanks.

I used an incremental build to run authenticated requests to Assembla, Beanstalk,. Bitbucket, Gitea, GitHub, GitLab, and Microsoft Visual Studio Online. All worked as expected.