Add option to skip deprecated config check during preinstall

Summary

Currently when installing the Omnibus package it will run gitlab-ctl config-check as part of it's preinstall process.

This check will fail when there's deprecated config present. While important and useful this can cause problems in specific situations such as when the user is looking to install the package only and skip reconfigure as an iterative step in their process.

This is typically the case when automating the process. Typically in this setup the process of Package Install (Repo, Deb, etc...), Config Setup and Reconfigure is followed across many nodes and having to update config first before anything else adds notable complexity. With this check it causes upgrades to fail at the very first step even though the config is due to be updated in the next and reconfigure is being held off.

When this does happen it's painful to address, especially on large multi-node systems. Nodes are left in a broken state and in turn require manual actions to remediate. The new packaged is "installed" in name but the internal config files internal config files (such as /opt/gitlab/embedded/nodes/{fqdn}json) (example) need to be updated to have the offending config removed or perform a full downgrade to proceed (which strictly you should only do with a database backup). This is not an ideal UX for our users.

Proposal

Proposal is to add a skip-config-check process much like several other parts of the preinstall script that allows for users to disable the check in select advanced circumstances.

This way it maintains the check for most users but allows for advanced use cases such as automation (GET) to disable when required.