[FEATURE] CLI option to apply change request locally

[michaelmelanson]

Is your feature request related to a problem? Please describe.
When I create a change request, I'd like to be able to test out the changes locally before they're applied. Currently the only way to do this is to manually apply environment variables.

Describe the solution you'd like
I'd like a new CLI flag for doppler run that applies the changes in the change request when running the command, e.g.:

doppler run --apply-cr=6d8e2041-de18-4b17-986f-0840faec579e ./server

This way I can test out a set of changes locally and make sure they have the effect I intend, without merging the PR and having it affect production systems.

Describe alternatives you've considered
The best alternative is to apply the changes manually, e.g.:

FOO=bar BAZ=quz doppler run ./server

However, this is error prone because you have to ensure manually that those environment variables match the change request, and that they're not going to be overwritten by doppler run.

Additional context
N/A