Include instructions to set a different DB for the migrations

In the deprecation warning and upgrade instructions.

Author: rosa

UPGRADING.md

@@ -1,11 +1,14 @@
 # Upgrading to version 1.3
-There's a new migration in this version that can be installed via
+There's a new migration in this version that can be installed via:
 ```bash
 bin/rails solid_queue:update
 ```
-which is a new generator to facilitate updates.
+which is a new generator to facilitate updates. This will use the `queue` database by default, but if you're using a different database name for Solid Queue, you can install the new migrations in the right place with:
+```bash
+DATABASE=your-solid-queue-db-name bin/rails solid_queue:update
+```
 
-Then, the migration needs to be run with
+Finally, the migration needs to be run with:
 ```bash
 bin/rails db:migrate
 ```

app/models/solid_queue/record.rb

@@ -25,7 +25,9 @@ def warn_about_pending_migrations
         SolidQueue.deprecator.warn(<<~DEPRECATION)
           Solid Queue has pending database migrations. To get the new migration files, run:
             rails solid_queue:update
-          And then:
+          which will install the migration under `db/queue_migrate`. To change the database, run
+            DATABASE=your-solid-queue-db rails solid_queue:update
+          Then, apply the migrations with:
             rails db:migrate
           These migrations will be required after version 2.0
         DEPRECATION