Eaiser GCP support

 It would be great to have an easier an easier way of running claude and targeting GCP endpoints.

Currently, to do this I need to run:

export CLAUDE_CODE_USE_VERTEX=1
export CLOUD_ML_REGION=us-east5
export ANTHROPIC_VERTEX_PROJECT_ID=<my-project-id-secret>
gcloud auth application-default login

claude

I either need to run 5 commands, or have a small script. And this small script then gets passed around many repositories and places.

It would be awesome if you made it possible with just one command, e.g.:

claude --use_vertex 1 --cloud_ml_region us-east5 --vertex_project_id secre-value-123