- Same format as used by the internal chroot mapping
- Map: source_path -> dest_path
- Example HCL:

client {
  chroot_env {
    "/etc" = "/etc"
    "/lib" = "/lib"
    "/opt/projects/foo/bin" = "/usr/bin"
  }
}

- Simplify map length check in Linux Executor
- Added a `chroot_env` test for config parser
- Moved `ChrootEnv` field from ExecutorCommand to ExecutorContext
- Added a test for `chroot_env` functionality

- Properly expects the hard-coded mounts (alloc, dev, and proc) and hardcoded local directories (local and tmp)
- Also verifies that etc contains only the requested paths