…for errors (ogizanagi)

This PR was squashed before being merged into the 5.3-dev branch.

Discussion
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[Console][Yaml] Linter: add Github annotations format for errors

| Q             | A
| ------------- | ---
| Branch?       | 5.x <!-- see below -->
| Bug fix?      | no
| New feature?  | yes <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | N/A <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT
| Doc PR        | TODO

Github actions [can write errors and warning](https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-commands-for-github-actions#setting-an-error-message) directly in their output, which result into annotations into the Github checks. It can even provide a filename, line & col number, allowing to display the annnotations inside the PR diff directly, at the right place.

More advanced usage of annotations can be made using the [API](https://docs.github.com/en/free-pro-team@latest/rest/reference/checks#list-check-run-annotations), but regarding the linters provided in Symfony components, it seems the shortcut using output is a great way to enhance the integration with Github Actions.

This PR starts by proposing these changes in the yaml linter:
- add the `github` format, which is the same as the `txt` one, except for errors and warning, for which we'll adapt the output to the Github annotations format.
- remove the `txt` format as default, and autodetect if the script is running in a Github action context, then use `github` format. If it's not, we fallback to `txt` as before.

Once we agree on the details, we could perform the same for other linters (xliff, twig, ...)

Here is a PR using it: ogizanagi/symfony-lint-gha-demo#2

and some screenshots:

| PR checks run | PR checks annotations | PR diff |
| -- | -- | -- |
| ![Capture d’écran 2020-11-04 à 09 37 07](https://user-images.githubusercontent.com/2211145/98089377-ed416600-1e82-11eb-8b10-40602b45efb1.png) | ![Capture d’écran 2020-11-04 à 09 37 28](https://user-images.githubusercontent.com/2211145/98089379-edd9fc80-1e82-11eb-8302-4e104abaeb2c.png) | ![Capture d’écran 2020-11-04 à 09 38 28](https://user-images.githubusercontent.com/2211145/98089381-edd9fc80-1e82-11eb-982a-9e4413ec30ba.png) |

~~(tests to add)~~

---

This was inspired by [PHPStan](https://github.com/phpstan/phpstan-src/blob/d77bd87da9f2fad0440fc1614158cdfc1b7cc88a/src/Command/ErrorFormatter/GithubErrorFormatter.php) which is already auto-adapting the output according to the CI, using https://github.com/OndraM/ci-detector

Commits
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f0bbdc8 [Console][Yaml] Linter: add Github annotations format for errors