Fixes: #9244

Description

This PR adds support for customizing the SSH and SCP commands used by the GitHub CLI's codespace functionality through environment variables. Users can now specify alternative SSH/SCP commands with additional options, providing greater flexibility and control over their codespace connections.

Features Added

• Added support for two new environment variables:

  • GH_CS_SSH_COMMAND: Allows customization of the SSH command used for gh cs ssh
  • GH_CS_SCP_COMMAND: Allows customization of the SCP command used for gh cs cp

• Implemented robust command-line parsing using the github.com/google/shlex library to handle quoted arguments and complex command structures

• Modified the newSSHCommand and newSCPCommand functions to incorporate arguments from the environment variables

Implementation Details

• The implementation uses the shlex library to parse command lines with quoted arguments, ensuring proper handling of complex command structures
• Custom arguments from environment variables are inserted at the beginning of the command arguments list
• Comprehensive unit tests were added to verify the functionality with various command formats

Example Usage

# Use SSH with verbose output
GH_CS_SSH_COMMAND="ssh -v" gh cs ssh -c my-codespace

# Use SSH with custom options
GH_CS_SSH_COMMAND="ssh -o LogLevel=DEBUG" gh cs ssh -c my-codespace

# Use a custom SSH binary with options
GH_CS_SSH_COMMAND="/path/to/custom/ssh -v -o IdentityFile=/custom/key" gh cs ssh -c my-codespace

# Similar usage for SCP commands
GH_CS_SCP_COMMAND="scp -v" gh cs cp -e README.md remote:/tmp/

Testing

1. Unit tests that verify the parsing of environment variables with various command formats
2. Manual testing with real codespaces, confirming that both SSH and SCP commands work as expected