Add docs for http server usage

[mohamedamer453]

Description

http sever configuration and running steps are documented in https://github.com/threefoldtech/grid3_client_ts/blob/development/docs/http_server.md however the commands/payloads or how to use the http server are not available.

[mohamedamer453]

Verified.

A usage section was added to the docs and it mentions the endpoint of the http server and how to use it with the desired module and method.

https://github.com/threefoldtech/tfgrid-sdk-ts/tree/development/packages/grid_http_server#usage