Build a working CI/CD-Pipeline

[christianhuth]

• [x] setup GitHub Pages (https://christianknell.github.io/helm-charts)
• [x] build stale workflow (https://github.com/marketplace/actions/close-stale-issues; https://github.com/actions/stale/blob/main/action.yml)
• [x] build linting and testing workflow (https://github.com/marketplace/actions/helm-chart-testing)
• [ ] build README-check workflow
• [ ] build values-schema check workflow
• [ ] build changelog creation workflow
• [x] build release2github workflow (https://github.com/stefanprodan/helm-gh-pages; https://github.com/marketplace/actions/helm-chart-releaser; https://helm.sh/docs/howto/chart_releaser_action/)
• [x] build release2chartmuseum workflow