undefined method `project_level?' for nil:NilClass

Summary

Trying to configure the instance-level integrations for Mattermost slash commands or Slack slash commands gives an undefined method error.

This is due to @service no longer existing in IntegrationsActions (used by admin and group integrations controller) after !60649 (merged).

Steps to reproduce

• Go to Admin -> Settings -> Integrations
• Click on Mattermost slash commands or Slack slash commands
• 💣 undefined method project_level? for nil:NilClass