Introduce :gitlab_geo schema for Geo tracking DB

What does this MR do and why?

Add a :gitlab_geo schema in lib/gitlab/database/gitlab_schemas.yml similar to the separation between :gitlab_main and :gitlab_ci to ensure our query analyzers catch any cross-joins and cross-transactions.

Related to #358422 (closed)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

ee/lib/ee/gitlab/database.rb

@@ -17,6 +17,27 @@ def all_database_names
           super + EE_DATABASE_NAMES
         end
 
+        override :check_postgres_version_and_print_warning
+        def check_postgres_version_and_print_warning
+          super
+        rescue ::Geo::TrackingBase::SecondaryNotConfigured
+          # ignore - happens when Rake tasks yet have to create a database, e.g. for testing
+        end
+
+        override :database_base_models
+        def database_base_models
+          @database_base_models_ee ||= super.merge(
+            geo: ::Geo::TrackingBase.connection_class? ? ::Geo::TrackingBase : nil
+          ).compact.with_indifferent_access.freeze
+        end
+
+        override :schemas_to_base_models
+        def schemas_to_base_models
+          @schemas_to_base_models_ee ||= super.merge(
+            gitlab_geo: [self.database_base_models[:geo]].compact
+          ).compact.with_indifferent_access.freeze
+        end
+
         def geo_database?(name)
           name.to_s == GEO_DATABASE_NAME
         end