[Docs] Migrate docs framework to Docusaurus (#282)

- Replace mkdocs with docosaurus (improved menu structure, ...)
- Structure docs into `Usage` and `Server Setup / Administration`
- Update favicon
- Create new pipeline-syntax page with all options and links to more detailed docs if available
- Add ci to publish to `woodpecker-ci.github.io`
- Deploy docs preview to surge for review
- Update start-page

Co-authored-by: 6543 <6543@obermui.de>

docs/.gitignore

@@ -0,0 +1,20 @@
+# Dependencies
+/node_modules
+
+# Production
+/build
+
+# Generated files
+.docusaurus
+.cache-loader
+
+# Misc
+.DS_Store
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*