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

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