feat(core): new util func to convert enum value slices to string slices

[rubenhoenle]

Description

This helps in the Terraform provider to use the enum values in the generated docs 😄

See for reference stackitcloud/terraform-provider-stackit#1055 where I duplicated this util func. But I think it belongs into here, the SDK core.

Checklist

• Issue was linked above
• No generated code was adjusted manually (check comments in file header)
• Changelogs
  • Changelog in the root directory was adjusted (see here)
  • Changelog(s) of the service(s) were adjusted (see e.g. here)
• VERSION file(s) of the service(s) were adjusted
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)