Added new configure install topic

Related to: https://gitlab.com/gitlab-org/gitlab-docs/-/merge_requests/1846

doc/administration/configure.md

+---
+stage: Enablement
+group: Distribution
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+type: reference
+---
+
+# Configure your GitLab installation
+
+Customize and configure your self-managed GitLab installation.
+
+- [Authentication](auth/README.md)
+- [Configuration](../user/admin_area/index.md)
+- [Repository storage](repository_storage_paths.md)
+- [Geo](geo/index.md)
+- [Packages](packages/index.md)