Create a web app with 1 page to load one file and execute one endpoint

Goal is to develop a web app with would process a XML file, prepare JSON based and execute specific endpoint.

1.GUI
One simple webpage without login and without auth. With 3 items:
- text input (to put auth. key),
- fille input to load file from disk,
- png logo.


2. Flow
- user fill "auth key" string value and load XML file from harddisk
- app will transform XML to JSON and execute POST endpoint
- if (SUCCESS) show "File is loaded correctly". If failed, show error description.


3. Source XML:
Attached "xml sample.xml"

4. Target endpoint
POST, https://api.infakt.pl/v3/invoices.json

JSON structure: "Invoice" object with number of "Services" subobject inside
(detail description: https://www.infakt.pl/developers/invoices/#create)

5. XML -> JSON
XML contains flat structure so you should create a collection of "Invoice" node (called "Faktura" in XML) and
add subitems as "Service" node (called "FakturaWiersz" in XML)