feat: add functionality to register plugins via http

Also:

- Add functionality for serving the responses from plugins
- Add tests for related methods and routes

Closes #2, #37

tsconfig.json

@@ -1,6 +1,7 @@
 {
   "extends": "./node_modules/@openstapps/configuration/tsconfig.json",
   "exclude": [
-    "./config/"
+    "./config/",
+    "./test/"
   ]
 }