Address soft deprecation of ActiveRecord::Base.connection

[joshuay03]

Related: #705

Refs:

• https://github.com/rails/rails/blob/b752c38e81a310c1aaca78c7cdd1784009ea189a/activerecord/lib/active_record/connection_handling.rb#L259
• https://github.com/rails/rails/blob/b752c38e81a310c1aaca78c7cdd1784009ea189a/activerecord/lib/active_record/connection_handling.rb#L293-L294

This will be soft deprecated in Rails 7.2.

The reason for this change is twofold.

1. We're running on Rails Edge with active_record.permanent_connection_checkout = :deprecated and this call to #connection was logged as a violation. Our goal is to configure this with :disallowed some day. Even if this needed to be a permanent checkout, connection should ideally be swapped with lease_connection (this would require a specific check to ensure the Rails dependency is >= 7.2).

2. Despite being called inside a with_connection block, this call actually leases a connection and doesn't return it back to the pool until the end of the request, which seems to have been intention behind ActiveRecord adapter: wrap all reads/writes in with_connection #705. This ensures we use the connection temporarily leased by with_connection.