[https://github.com/tracim/tracim/issues/825] config is now a json file instead of js file

frontend/.gitignore

 dist/asset/tracim.app.entry.js
 dist/asset/tracim.vendor.bundle.js
 dist/asset/images/
-configEnv.js
+configEnv.json

frontend/configEnv.js.sample

-export const apiUrl = 'http://localhost:6543/api/v2'

frontend/configEnv.json

+{
+  "apiUrl": "http://localhost:6543/api/v2"
+}

frontend/configEnv.json.sample

+{
+  "apiUrl": "http://localhost:6543/api/v2"
+}

frontend/src/helper.js

-import { apiUrl as configApiUrl } from '../configEnv.js'
+const configEnv = require('../configEnv.json')
 
 export const FETCH_CONFIG = {
   headers: {
     'Accept': 'application/json',
     'Content-Type': 'application/json'
   },
-  apiUrl: configApiUrl,
+  apiUrl: configEnv.apiUrl,
   mockApiUrl: 'http://localhost:3001' // @todo: better to use one url only and use proxy on mock api to point to real api (if implemented)
 }