DEV: Fix mismatched column types (#868)

The primary key is usually a bigint column, but the foreign key columns
are usually of integer type. This can lead to issues when joining these
columns due to mismatched types and different value ranges.

This was using a temporary plugin / test API to make tests pass, but it
is safe to alter "ai_document_fragment_embeddings" and
"rag_document_fragments" tables because they usually have less than 1M
rows and migration is going to be fast.

Depending on the size of the community, "classification_results" table
may have more than 1M rows and the migration will lock the table for a
longer time. However, classification runs in background jobs and they
will be automatically retried if they fail due to the lock, which makes
it acceptable.

db/migrate/20241025135522_alter_ai_ids_to_bigint.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class AlterAiIdsToBigint < ActiveRecord::Migration[7.1]
+  def up
+    change_column :ai_document_fragment_embeddings, :rag_document_fragment_id, :bigint
+    change_column :classification_results, :target_id, :bigint
+    change_column :rag_document_fragments, :target_id, :bigint
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

spec/plugin_helper.rb

@@ -17,14 +17,4 @@ module DiscourseAi::ChatBotHelper
   end
 end
 
-RSpec.configure do |config|
-  config.include DiscourseAi::ChatBotHelper
-
-  config.before(:suite) do
-    if defined?(migrate_column_to_bigint)
-      migrate_column_to_bigint(RagDocumentFragment, :target_id)
-      migrate_column_to_bigint("ai_document_fragment_embeddings", "rag_document_fragment_id")
-      migrate_column_to_bigint(ClassificationResult, :target_id)
-    end
-  end
-end
+RSpec.configure { |config| config.include DiscourseAi::ChatBotHelper }