Feature request: support using environment variables for Personal Access Tokens (PATs).

[doggy8088]

Rationale:

1. Environment variables raise security by removing hard-coded secrets. A PAT stored in an environment variable eliminates the need to embed credentials in scripts or configuration files. This allows each environment—development, testing, production—to supply its own token without code changes.

2. Environment variables streamline development workflows. Multiple developers can work in different environments while relying on the same code path; only the environment variable differs. CI/CD pipelines can inject the correct PAT at runtime, avoiding manual substitution and reducing deployment friction.

3. Environment-variable–based PATs integrate cleanly with containerized execution. Docker and Kubernetes can inject secrets into containers through their native mechanisms, keeping tokens isolated while maintaining controlled access for automation and tooling that depend on tfs-cli.

So, supporting PAT authentication through environment variables removes hard-coded credentials, simplifies configuration across environments, and aligns tfs-cli with common DevOps practices.