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.

.gitlab/issue_templates/Geo Replicate a new Git repository type.md

@@ -64,7 +64,7 @@ For more information, see the [Enable Geo migrations to use Migration[2.0]](http
     disable_ddl_transaction!
 
     def up
-      ActiveRecord::Base.transaction do
+      ApplicationRecord.transaction do
         create_table :cool_widget_registry, id: :bigserial, force: :cascade do |t|
           t.bigint :cool_widget_id, null: false
           t.datetime_with_timezone :created_at, null: false