feat(platform/gitlab): confidential issues (#12728)

docs/usage/configuration-options.md

lib/config/options/index.ts

lib/config/types.ts

lib/platform/gitlab/__snapshots__/index.spec.ts.snap

lib/platform/gitlab/index.spec.ts

lib/platform/gitlab/index.ts

lib/platform/types.ts

lib/workers/repository/dependency-dashboard.ts

lib/workers/repository/error-config.ts

lib/workers/repository/process/deprecated.ts