add versioning support to the API

src-ui/src/environments/environment.prod.ts

@@ -1,6 +1,7 @@
 export const environment = {
   production: true,
   apiBaseUrl: "/api/",
+  apiVersion: "1",
   appTitle: "Paperless-ng",
   version: "1.2.1",
   webSocketHost: window.location.host,

src-ui/src/environments/environment.ts

@@ -5,6 +5,7 @@
 export const environment = {
   production: false,
   apiBaseUrl: "http://localhost:8000/api/",
+  apiVersion: "1",
   appTitle: "Paperless-ng",
   version: "DEVELOPMENT",
   webSocketHost: "localhost:8000",