feat: Enable Slack Integration in all channels (#1175)

db/migrate/20200828175931_add_external_source_ids_to_messages.rb

@@ -0,0 +1,16 @@
+class AddExternalSourceIdsToMessages < ActiveRecord::Migration[6.0]
+  def change
+    add_column :messages, :external_source_ids, :jsonb, default: {}
+    migrate_slack_external_source_ids
+  end
+
+  def migrate_slack_external_source_ids
+    Message.where('source_id LIKE ?', 'slack_%').find_in_batches do |message_batch|
+      message_batch.each do |message|
+        message.external_source_id_slack = message.source_id.split('slack_')[1]
+        message.source_id = nil
+        message.save!
+      end
+    end
+  end
+end