Add DISABLE_SOLID_QUEUE environment variable

[theseanything]

Allow disabling solid queue puma plugin via environment variable.
By default loads solid queue plugin in production mode unless
DISABLE_SOLID_QUEUE is set to "true".

This is used to disable the solid queue supervisor process from
our web server ECS tasks. This allows us to test these changes
in non-production environments. This is part of work moving the
solid queue workers into a separate ECS task.

[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.

[whi-tw]

@theseanything if happy, could you please get this merged in, so we can start testing?

[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