Log when we return in Integration#async_execute

What does this MR do and why?

This MR adds a log to Integration#async_execute when we return without queuing a worker. This log is to gather data for #382999 as to how useful the optimisation in that issue could be.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. From your /gitlab directory, in a console run: tail -f log/integrations_json.log
2. Configure a Jenkins project integration, go to /<PROJECT_FULL_PATH>/-/settings/integrations/jenkins/edit
   • For Jenkins server URL enter https://example.com
   • For Project name enter any name
   • Click Save
3. Close an issue in the project

You will see a log like:

{
  "severity": "INFO",
  "time": "2024-07-12T02:33:02.147Z",
  "correlation_id": "01J2JCJSBN5B1A7PB0J18AH38A",
  "meta.caller_id": "GraphqlController#execute",
  "meta.remote_ip": "127.0.0.1",
  "meta.feature_category": "team_planning",
  "meta.user": "root",
  "meta.user_id": 1,
  "meta.client_id": "user/1",
  "integration_class": "Integrations::Jenkins",
  "integration_id": 663,
  "project_id": 163,
  "project_path": "imports/luke-test-1-July",
  "message": "async_execute did nothing due to event not being supported",
  "event": "issue"
}

Related to #382999