Add dedicated tutorial label

[ccremer]

I feel it's starting to make sense to better highlight how-tos and tutorial updates

Note: the label tutorial can be also applied for How-to pages, as they are kind of tutorials also, just very focused on specific topics.

Checklist

• Try to isolate changes into separate PRs (to build a better changelog).
• Categorize the PR by setting a good title and adding one of the labels:
  change, decision, requirement/quality, requirement/functional, dependency
  as they show up in the changelog
• Link this PR to related issues if applicable.