chore: improve rendering of documentation

[aepfli]

With this pull request, we're further improving the rendering of the community files.

The layout of all files has been improved, and links are working for all files. And a Netlify build is ready to be used so we can display the page and check the community files and how they will be rendered, eg. within the KLT.

see: https://deploy-preview-3--keptn-community.netlify.app/ rendered from the same branch within my fork