techdocs: add extensions for techdocs addons (#28644)

* techdocs: add extensions for techdocs addons

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

* techdocs: add blueprint extension for techdocs addons

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

* techdocs: move addons blueprint to alpha

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

* techdocs: add addon extensions for new frontend system and add docs

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

* techdocs: fix addon modules naming patterns

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

* techdocs: update test utils with entity presentation api

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

---------

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

plugins/techdocs-react/package.json

@@ -14,9 +14,7 @@
     ]
   },
   "publishConfig": {
-    "access": "public",
-    "main": "dist/index.esm.js",
-    "types": "dist/index.d.ts"
+    "access": "public"
   },
   "keywords": [
     "backstage",
@@ -30,8 +28,23 @@
   },
   "license": "Apache-2.0",
   "sideEffects": false,
+  "exports": {
+    ".": "./src/index.ts",
+    "./alpha": "./src/alpha.ts",
+    "./package.json": "./package.json"
+  },
   "main": "src/index.ts",
   "types": "src/index.ts",
+  "typesVersions": {
+    "*": {
+      "alpha": [
+        "src/alpha.ts"
+      ],
+      "package.json": [
+        "package.json"
+      ]
+    }
+  },
   "files": [
     "dist"
   ],
@@ -49,6 +62,7 @@
     "@backstage/config": "workspace:^",
     "@backstage/core-components": "workspace:^",
     "@backstage/core-plugin-api": "workspace:^",
+    "@backstage/frontend-plugin-api": "workspace:^",
     "@backstage/version-bridge": "workspace:^",
     "@material-ui/core": "^4.12.2",
     "@material-ui/styles": "^4.11.0",