[ENH] - Add `--dry-run` option to qhub installation

[viniciusdc]

Feature description

The Terraform Provision and Terraform Apply steps in the qhub deploy could be executed as a dry run, just like running the terraform plan command.

The dry run would refresh the state file (if present) and generate a deployment plan based on the provided qhub infrastructure but not apply the plan.

Value and/or benefit

The benefits of doing so would be:

• Generating the qhub full infrastructure model and exporting/importing it to proper locations if needed -- infra cost might be able to use this for better predictions
• CI testing, we could then mimic the installation process and run these (without deploying an instance) into different architectures, like Windows, Linux, and macOS. This would help cathing situations such as https://github.com/Quansight/qhub/issues/1367
• We would also be able to inspect the outputted plan and compare it with a pre-defined test template to assert versions, providers, and config maps are all well-defined and present.

Anything else?

https://github.com/Quansight/qhub/issues/93 initially proposed this