Add possibility to detect tutorials by frontmatter

[Dr-Electron]

As we have tutorial and how-to section it would make sense to include them automatically to the tutorial plugin

[Dr-Electron]

If the file is just a single page inside tutorials for example, that's it. We only import that file with it's image and description and tags (tags like the project should be added automatically, maybe we should also fail the build on missing tags?).

If the page is part of a subsection inside of tutorials like subsection/page1, we should import all the files at the same level as part of this tutorial.

For now I'm not sure if we need multipage support. So a first version without it should be fine

[jlvandenhout]

Several questions:

1. Is the goal to not have to configure this plugin at all in the case where we will use this frontmatter? Or do you mean we configure this plugin with something like path: 'path/to/tutorials/folder' and it would add all of the pages below it that have a valid frontmatter?
2. Previously we concluded doc tags can't be used for tutorial tags, because they serve different purposes, so we should probably add our own property to the frontmatter, something like tutorialTags or something?
3. Not sure how to approach the automatic configuration of the project tag tbh, because the tutorial plugin can't know anything about the doc plugin that adds the actual page during build (that's why we need to hardcode the url to the doc in the current implementation). The tutorial page could do that client side probably 🤔

[jlvandenhout]

So I guess from the above we could have a tutorial doc tag that the tutorials page can filter by and a tutorialTags frontmatter property to add tutorial tags to the doc (or even just the presence of tutorialTags is enough 🤔 ). Then we don't need to configure this plugin at all and the tutorial page should be able to figure everything out client side, including the project as it will be the base of the path where the doc lives (although this is not very robust and depends on convention)