Update and cleanup docs (#851)

- migrate step conditions back into pipeline syntax, but show 2-4 level in toc to be able to see `when` keywords
- create new backend section in admin docs
- update docusaurus
- remove prefix docker of container / container-image where possible
- replace terms SCM, VCS, Github with [forge](https://en.wikipedia.org/wiki/Forge_(software))
- add darkmode favicon variant

docs/plugins/woodpecker-plugins/package.json

@@ -9,17 +9,17 @@
     "build": "tsc && tsc -p tsconfig.jsx.json"
   },
   "devDependencies": {
-    "@docusaurus/module-type-aliases": "^2.0.0-beta.15",
-    "@docusaurus/theme-classic": "^2.0.0-beta.15",
-    "@docusaurus/types": "^2.0.0-beta.15",
+    "@docusaurus/module-type-aliases": "^2.0.0-beta.18",
+    "@docusaurus/theme-classic": "^2.0.0-beta.18",
+    "@docusaurus/types": "^2.0.0-beta.18",
     "@octokit/openapi-types": "^11.2.0",
     "@octokit/rest": "^18.12.0",
-    "@tsconfig/docusaurus": "^1.0.4",
-    "@types/marked": "^4.0.1",
+    "@tsconfig/docusaurus": "^1.0.5",
+    "@types/marked": "^4.0.3",
     "clsx": "^1.1.1",
-    "concurrently": "^6.4.0",
-    "marked": "^4.0.5",
-    "typescript": "^4.5.2"
+    "concurrently": "^7.0.0",
+    "marked": "^4.0.12",
+    "typescript": "^4.6.3"
   },
   "peerDependencies": {
     "react": "^17.0.2",