Add `feast plan`

**Is your feature request related to a problem? Please describe.**
When we wanted to move from prototyping to production, we had to execute multiple times `feast apply` locally and in our CI/CD environment. We ended up deleting everything when we were just trying things differently. It would have been nice to just pass an option like `--dry-run` to print but not execute what `feast apply` wants to do

**Describe the solution you'd like**
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A very common option would be to add the option `--dry-run` to `feast apply`.
Another possible one is to create another command (eg: `feast plan`)

**Describe alternatives you've considered**
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**Additional context**
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