New authentication flow

We've added an authentication flow, where you can generate a temporary API token and use it for every API request.

API Reference:

https://docs.beeteller.com/reference/authenticate

To use this new API token, you must set "Bearer" prefix in the Authorization header, for every protected endpoint. E.g.:

curl --request GET \
     --url https://api-test.beeteller.com/gtw/2.1/payment/ \
     --header 'accept: application/json' \
     --header 'content-type: application/json' \
     --header 'Authorization: Bearer YOUR_GENERATED_TOKEN' \
'