Thingsboard API Proy

A simple API proxy to make thingsboard managable by the Terraform Restful Provider.

The concrete work includes:

1. Turns the authentication request from the Terraform Restful Provider in the urlencoded style, to its equivalent in body style, which is expected by the thingsboard API.
2. Turns PUT API request that is used by the Terraform Restful Provider to update a resource, to its equivalent POST form, which is expected by the thingsboard API.