`bitops plan` option

[josh-bitovi]

When we get lots of inheritance and charts/values/secrets changing at once, it'd be nice to see what's actually going to change before approving the merge/deploy.

Terraform supports this with terraform plan. It'd be nice if bitops could support this for all tools, as they all support some form of "dry run" that we could use for this functionality.

We could also hook into GitLab pipelines for manual approval (which would end up giving us functionality like this bot).

• helm upgrade supports --dry-run and --template (latter dumps the templates, former just catches errors?)
• ansible supports --check

Other stuff to think about:

• What doesn't this cover?
• What about secrets? Would we need something like GitLab's masked variables to ensure those don't make it into build logs?
• Do we need hooks? Would they be a way of emulating GitLab's "manual approval" stage?
• Would running BitOps locally against minikube be more useful instead?