feat: Add support for persistent copilot threads and messages (#11489)

The agents can see the previous conversations with the copilot if needed
with this change. We would have to cleanup the data after a while. For
now, that is not considered.

This PR adds:
- A new model for copilot_threads (intentionally named thread instead of
conversation to avoid confusion), copilot_messages
- Add the controller to fetch previous threads and messages.

db/migrate/20250512231036_create_copilot_threads.rb

@@ -0,0 +1,14 @@
+class CreateCopilotThreads < ActiveRecord::Migration[7.0]
+  def change
+    create_table :copilot_threads do |t|
+      t.string :title, null: false
+      t.references :user, null: false, index: true
+      t.references :account, null: false, index: true
+      t.uuid :uuid, null: false, default: 'gen_random_uuid()'
+
+      t.timestamps
+    end
+
+    add_index :copilot_threads, :uuid, unique: true
+  end
+end

db/migrate/20250512231037_create_copilot_messages.rb

@@ -0,0 +1,13 @@
+class CreateCopilotMessages < ActiveRecord::Migration[7.0]
+  def change
+    create_table :copilot_messages do |t|
+      t.references :copilot_thread, null: false, index: true
+      t.references :user, null: false, index: true
+      t.references :account, null: false, index: true
+      t.string :message_type, null: false
+      t.jsonb :message, null: false, default: {}
+
+      t.timestamps
+    end
+  end
+end