Create GitHub Action to check view on PRs & merges

[wibeasley]

As recommended in https://github.com/cran-task-views/ctv/blob/main/Documentation.md#using-github-actions-to-validate-task-views.

The GitHub Action can be installed as described in the action/README. In its current version, it is automatically run at push or merge requests performed in the main branch of the task view file. More general guidance about GitHub Actions can be found in the the GitHub documentation.

[pachadotdev]

good idea! I do this manually once a month (and with notepad, I'm just implementing VS Code)