[Tracking] `devcontainer features test` improvements

An issue collecting various improvements that can be made for the `features test...` command. The command is still experimental and under active development.

- [x] `remoteUser`, `containerUser`, or a container with a default non-root user are failing with a permissions issue when included in a scenario
- [x] Scenario tests appear to run as `root` even when `-u` specified in command line
- [ ] Feature values specified in scenario.json do not appear to be space escaped ("a b" ends up as "a")
- [x] `-f` prevents other parameters after it from being used since it treats them all as part of the array. Makes it impossible to pass in the require parameters.
- [x] Document all command functionality (ie: https://github.com/devcontainers/spec/discussions/113#discussioncomment-3830454) (https://github.com/devcontainers/cli/pull/219)
- [ ] If there is a scenario.json file and no test.sh, the test will not run unless `--skip-autogenerated` is set. We should be smarter about this
- [x] The one positional argument (path to collection) is required and doesn't use the default value (cwd)
- [x] Support `build.dockerfile` - Currently errors since Dockerfile referenced is not copied to temp location
- [x] Allow specifying a specific scenario to test via the CLI (helps if only one of several is failing)
- [ ] #438
- [ ] Output results to stdout so you can pipe to a log file w/o getting the entire build output (appears to go to stderr right now)
- [ ] Be able to override a certain base image <-> feature combos in the autogenerated tests (https://github.com/devcontainers/features/pull/116#pullrequestreview-1090984379)
- [x] https://github.com/devcontainers/cli/issues/163 / https://github.com/devcontainers/cli/issues/217
- [x] https://github.com/devcontainers/spec/discussions/114#discussioncomment-4031722
- [ ] https://github.com/devcontainers/cli/issues/334
- [ ] https://github.com/devcontainers/cli/issues/409
- [ ] https://github.com/devcontainers/cli/issues/448

`devcontainer features test` コマンドから始め、`scenario.json`、`test.sh`、stdout、自動生成テストに関する未チェック項目を確認します。リンクされている CLI issue とディスカッションを文脈として参照し、その後、範囲を限定した改善を 1 つ選び、その動作が実装され、検証されていることを完了の条件として定義します。

索引モデルが issue の本文から書いたものです。