Create SolidQueue healthcheck process

[sarahseewhy]

What problem does this pull request solve?

Trello: https://trello.com/c/f7js82Cm/635-run-solid-queue-as-its-own-ecs-task

We want to run the Solid Queue worker as a separate ECS task (see this PR: govuk-forms/forms-deploy#1558). The worker ECS task needs a healthcheck to verify the task is running ok.

This pull requests implements a "lifecycle hook" that creates a healthcheck file when Solid Queue starts and removes the file when the process stops.

According to the Solid Queue README a lifecycle hook is the encouraged approach for this type of scenario (see README).

Thanks to @lfdebrux's research I've implemented something similar to SideKiq's file-based readiness probe (see README).

I've tested this locally and in dev. The file gets created when the process starts and removed when the process stops. When deployed along side the relevant infrastructure changes the ECS tasks start running and achieve a Healthy "Health status".

[lfdebrux]

Looks good to me! I just have a few style comments 😁

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

🎉 A review copy of this PR has been deployed! It is made of up two components

1. A review copy of forms-runner
2. A production copy of forms-admin

Important

Not all of the functionality of forms-runner is present in review apps.
Functionality such as sending emails, file upload, and S3 submission types are
deliberately disabled for the sake of simplifying review apps.

You should use the full dev environment to test the functionality which is disabled here.

It may take 5 minutes or so for the application to be fully deployed and working. If it still isn't ready
after 5 minutes, there may be something wrong with the ECS task. You will need to go to the integration AWS account
to debug, or otherwise ask an infrastructure person.

For the sign in details and more information, see the review apps wiki page.