Carefully handle overwriting secrets in Fireworks account

[dphuang2]

• Introduced --env-file argument in the CLI for specifying the path to the .env file containing secrets.
• Refactored the upload process to include a new function upload_secrets_to_fireworks that handles the uploading of secrets.
• Updated the upload_command to optionally skip secret uploads if already handled.
• Enhanced the evaluator upload process to ensure secrets are uploaded before ensuring evaluator existence.

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Note

Improves secrets management and evaluator creation flow.

• Adds --env-file to create rft for specifying a secrets file; secrets are now uploaded before evaluator checks/uploads
• Introduces upload_secrets_to_fireworks and integrates it into both upload (optional via skip_secrets) and create rft paths
• Detects existing Fireworks secrets via get_fireworks_secret, deselects them by default in prompts, and adds double-confirmation before overwriting
• Enhances selection UX: marks existing secrets as [exists], defaults to only new secrets in non-questionary fallback, and improves masked logging
• Updates _upload_and_ensure_evaluator to accept env_file/non_interactive and to call upload_command(..., skip_secrets=True)

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