Abstract Publisher APIs from the router

1. Move fetchMetadata and serve static files to local publisher
2. Create factory class to create publishers based on app cofig

packages/techdocs-common/package.json

@@ -39,14 +39,16 @@
     "@backstage/backend-common": "^0.3.2",
     "@backstage/catalog-model": "^0.3.1",
     "@backstage/config": "^0.1.1",
+    "@types/dockerode": "^2.5.34",
+    "@types/express-serve-static-core": "^4.17.14",
     "cross-fetch": "^3.0.6",
     "dockerode": "^3.2.1",
+    "express": "^4.17.1",
     "fs-extra": "^9.0.1",
     "git-url-parse": "^11.4.0",
     "js-yaml": "^3.14.0",
     "mock-fs": "^4.13.0",
     "nodegit": "^0.27.0",
-    "@types/dockerode": "^2.5.34",
     "winston": "^3.2.1"
   },
   "devDependencies": {