Optimize GitHub action workflow scope

[svengreb]

Currently all jobs are summarized in the ci workflow but not separated by their scope, e.g. only Node specific tasks. The workflow is also not optimized to only run when specific files have been changed which results in false-positive executions and wastes limited free tier and developer time.
Therefore the ci workflow will be optimized.

CI Node

A new ci-node workflow will…

• only run when any *.js, *.json, *.md, *.yaml and *.yml file has been modified. This matches the lint-staged, Prettier and remark configurations. See the extensive GitHub action documentations about on.<push|pull_request>.paths and the filter pattern cheat sheet for more details.
• only run for ubuntu-latest instead of a matrix with macos-latest and windows-latest since there is no platform specific code yet.
• use cache npm dependencies which is possible as of actions/setup-node@v2.2.0.