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/app/models/geo/tracking_base.rb

@@ -6,9 +6,6 @@ module Geo
   class TrackingBase < ApplicationRecord
     self.abstract_class = true
 
-    NOT_CONFIGURED_MSG     = 'Geo secondary database is not configured'
-    SecondaryNotConfigured = Class.new(StandardError)
-
     if ::Gitlab::Geo.geo_database_configured?
       connects_to database: { writing: :geo, reading: :geo }
     end
@@ -20,16 +17,8 @@ def self.connected?
     end
 
     def self.connection
-      unless ::Gitlab::Geo.geo_database_configured?
-        message = NOT_CONFIGURED_MSG
-        message = "#{message}\nIn the GDK root, try running `make geo-setup`" if Rails.env.development?
-        raise SecondaryNotConfigured, message
-      end
-
       # Don't call super because LoadBalancing::ActiveRecordProxy will intercept it
       retrieve_connection
-    rescue ActiveRecord::NoDatabaseError
-      raise SecondaryNotConfigured, NOT_CONFIGURED_MSG
     end
 
     class SchemaMigration < TrackingBase