Add --dry-run option to cf push (could be reused for plugins like cf bg-deploy as well)

[rufreakde]

What's the user value of this feature request? Easy and fast validation of deployments improving developers efficiency/productivity and also reduced human error.

Who is the functionality for? Everyone using cf on daily basis, especially for learning beginners.

How often will this functionality be used by the user? Daily

Who else is affected by the change? Every developer using the CLI to push changes especially to important spaces this would provide security.

Describe the solution you'd like just add a --dry-run parameter to the cf push command to simulate a push with the specified settings )similar to helm install --dry-run)

Describe alternatives you've considered 0 (the simpler and clearer the solution the better for the users of the CLI)

Additional context Best practice for deployment in cloud spaces like k8s and helm. Actually it would be nice for all kinds of deployments to have a --dry-run option consistently across the board.

Note: As of the GA of the v7 CLI, the v6 line is no longer under active development and will be updated only to patch CVEs or fix severe blocking defects with no workarounds.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/177962335

The labels on this github issue will be updated when the story is started.