Added environments for http requests

http-requests/calculate-result.http

@@ -1,4 +1,4 @@
-POST http://localhost:12000/wahlrecht/v1/calculate
+POST {{backend}}/wahlrecht/v1/calculate
 Content-Type: application/json
 
 {

http-requests/get-elections.http

@@ -0,0 +1,2 @@
+GET {{backend}}/wahlrecht/v1/elections
+Content-Type: application/json

http-requests/http-client.env.json

@@ -0,0 +1,8 @@
+{
+  "dev": {
+    "backend": "http://localhost:12000"
+  },
+  "prod" : {
+    "backend": "https://api.2martens.de"
+  }
+}