Resolve "Fix `Gitlab::Database::SchemaCacheWithRenamedTable` does not work with many databases"

What does this MR do and why?

Fix Gitlab::Database::SchemaCacheWithRenamedTable to work with many databases

Instead of getting the connection from ActiveRecord::Base, we use the connection from ActiveRecord::ConnectionAdapters::SchemaCache. Schema cache will return the proper connection based on the database context.

https://github.com/rails/rails/blob/main/activerecord/lib/active_record/connection_adapters/schema_cache.rb#L36

Screenshots or screen recordings

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How to set up and validate locally

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

1. Add to TABLES_TO_BE_RENAMED. A good one is:

   TABLES_TO_BE_RENAMED = { 'services' => 'integrations' }.freeze

2. Setup multiple databases

3. Only in gitlabhq_development_ci, create the services view with CREATE VIEW services AS SELECT * FROM integrations;

4. Check the :renamed_tables_cache is distinct

5. Cleanup. Drop the services view in the gitlabhq_development_ci database with DROP VIEW services;

Before:

[1] pry(main)> Ci::ApplicationRecord.retrieve_connection.schema_cache.send :renamed_tables_cache
=> {}
[2] pry(main)> ApplicationRecord.retrieve_connection.schema_cache.send :renamed_tables_cache
=> {}

After:

[1] pry(main)> ApplicationRecord.retrieve_connection.schema_cache.send :renamed_tables_cache
=> {}
[2] pry(main)> Ci::ApplicationRecord.retrieve_connection.schema_cache.send :renamed_tables_cache
=> {"services"=>"integrations"}

[4] pry(main)> Ci::ApplicationRecord.retrieve_connection.schema_cache.send :underlying_table, 'services' 
=> "integrations"

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.

Related to #336899 (closed)