Remove --promote flag from model push

[cretz]

🚀 What

--promote is just shortcut for --environment production and we don't want the separate flag anymore.

💻 How

Removed the --promote flag

🔬 Testing

Adjusted tests

[Copilot]

Pull request overview

Removes the --promote flag from baseten model push, standardizing on --environment production for production pushes and simplifying flag handling in the model push command.

Changes:

• Removed --promote from ModelPushFlags and eliminated promote-specific handling/validation in the model push implementation.
• Updated E2E coverage to use --environment production for production pushes.
• Adjusted unit tests by removing validation specific to the deleted --promote flag.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
cmd/command.model.go	Removes the --promote flag from the CLI flag definitions for model push.
internal/cmd/command.model_push.go	Deletes promote/environment mutual-exclusion validation and promote-to-production flag handling.
internal/cmd/command.model_push_test.go	Removes the unit test that asserted --promote and --environment were mutually exclusive.
internal/e2e-tests/model_test.go	Updates E2E calls to push to production via --environment production instead of --promote.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.