Conditionally use different sbt plugin

What does this MR do?

This merge request allows us to conditionally use a different sbt plugin declaration for our Debian image in order to allow us to support Java 21 sbt projects. It does this by using code inside plugins.sbt that selects which version of the plugin to use. Currently support is limited to sbt 1.9.7.

What are the relevant issue numbers?

• Dependency Scanning and License Scanning Java 2... (gitlab-org/gitlab#421174 - closed) • Philip Cunningham • 16.6 • On track

What are the related merge requests?

• Add sbt for Java 21 in non-FIPS offline environ... (!596 - closed) • Philip Cunningham • 16.6

Notes

Demonstrates an alternative path forward for:

• Gemnasium fails when running sbt dependencyDot:... (gitlab-org/gitlab#390287 - closed) • Olivier Gonzalez • 16.10 • On track

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer