[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/src/css/custom.css

@@ -0,0 +1,28 @@
+/**
+ * Any CSS included here will be global. The classic template
+ * bundles Infima by default. Infima is a CSS framework designed to
+ * work well for content-centric websites.
+ */
+
+/* You can override the default Infima variables here. */
+:root {
+  --ifm-color-primary: #4caf50; /* #25c2a0 */
+  --ifm-color-primary-dark: rgb(33, 175, 144);
+  --ifm-color-primary-darker: rgb(31, 165, 136);
+  --ifm-color-primary-darkest: rgb(26, 136, 112);
+  --ifm-color-primary-light: rgb(70, 203, 174);
+  --ifm-color-primary-lighter: rgb(102, 212, 189);
+  --ifm-color-primary-lightest: rgb(146, 224, 208);
+  --ifm-code-font-size: 95%;
+}
+
+.docusaurus-highlight-code-line {
+  background-color: rgba(0, 0, 0, 0.1);
+  display: block;
+  margin: 0 calc(-1 * var(--ifm-pre-padding));
+  padding: 0 var(--ifm-pre-padding);
+}
+
+html[data-theme='dark'] .docusaurus-highlight-code-line {
+  background-color: rgba(0, 0, 0, 0.3);
+}