feat(codex): add Codex CLI feature and related tests

[jsburckhardt]

This pull request introduces a new feature for integrating the Codex CLI into the project. The changes include adding Codex as a supported tool, updating documentation, and implementing installation and testing scripts for the Codex CLI.

Additions to Codex CLI Support:

• Feature Definition: Added a new devcontainer-feature.json file for Codex, defining its metadata and purpose as a CLI for AI-assisted coding. (src/codex/devcontainer-feature.json)
• Installation Script: Implemented an install.sh script to automate the installation of the latest Codex CLI release, including handling various OS/architecture combinations and release asset formats. (src/codex/install.sh)

Documentation Updates:

• README Enhancements: Updated the README.md to include Codex CLI in the list of features and added instructions for running Codex inside the container. (README.md) [1] [2]

Workflow and Testing Updates:

• Workflow Update: Added Codex to the list of tools in the GitHub Actions workflow configuration. (.github/workflows/test.yaml)
• Testing Scripts:
  • Updated global test scripts to include Codex version checks. (test/_global/all-tools.sh, test/_global/scenarios.json) [1] [2]
  • Added a dedicated test script for Codex to verify its functionality. (test/codex/test.sh)