Add safe navigators to sidekiq monitoring settings

What does this MR do and why?

Fixes #349143 (closed)

Not all development environments set the default values for the new Sidekiq settings. For example, in GDK you can disable automatically updating your gitlab.yml with new settings, and that would mean they have to be manually added.

We add safe navigators so Sidekiq doesn't crash when the settings are not set

How to set up and validate locally

1. Run Sidekiq (gdk start rails-background-jobs)

2. Profit

MR acceptance checklist

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