Allow to report the database reference

From the guides https://guides.rubyonrails.org/active_record_multiple_databases.html on multiple databases, we have the following `database.yml` file:
```
production:
primary:
database: my_primary_database
user: root
adapter: mysql
primary_replica:
database: my_primary_database
user: root_readonly
adapter: mysql
replica: true
animals:
database: my_animals_database
user: animals_root
adapter: mysql
migrations_paths: db/animals_migrate
animals_replica:
database: my_animals_database
user: animals_readonly
adapter: mysql
replica: true
```
I would like to signal which database the query is running. Given the replicas have the same database name, the `database` comment on marginalia won't work.
Is it possible to add the `animals` and `animals_replica` names to the comments?

Start with the Active Record multiple-databases guide and the database.yml example, then inspect how Marginalia currently derives its database comment for ActiveRecord SQL queries. Determine how the animals and animals_replica references are exposed to the query, and consider the work done when comments distinguish those references even when their database names match.

Written by the indexing model from the issue text.