Load env.runit in Rails console

What does this merge request do and why?

Closes ENV vars in rails console (#2008 - closed)

env.runit

GITLAB_SIMULATE_SAAS=1

shinya@shinya-XPS-15-9530:~/gitlab-development-kit/gitlab$ gdk rails c
--------------------------------------------------------------------------------
 Ruby:         ruby 3.1.4p223 (2023-03-30 revision 957bb7cb81) [x86_64-linux]
 GitLab:       16.7.0-pre (56a7aff8333) EE
 GitLab Shell: 14.31.0
 PostgreSQL:   14.9
-------------------------------------------------------------[ booted in 5.04s ]
Loading development environment (Rails 7.0.8)
[1] pry(main)> ENV['GITLAB_SIMULATE_SAAS']
=> "1"

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.