Add ability to send an HTTP POST request to Ambi backend endpoint

[jhodapp]

Summary

To wrap up our ESP32 WiFi proof-of-concept, the final piece is to add the ability to make an HTTP POST request with a JSON payload to an Ambi backend instance.

Feature specifics

Add a function to send an HTTP POST request to Ambi backend endpoint:

1. Function should take the following parameters and send off a POST request to host
   • Client socket
   • Host IP address
   • HTTP port of host
   • HTTP request path (the Ambi API endpoint path minus host IP/port)
2. It should send a JSON payload as part of the HTTP body
   • See the ambi_mock_client source and example output for reference
   • Identify and import a simple JSON serializer Rust crate that doesn't use stdlib
   • Identify and import a simple HTTP client Rust crate that does not use Rust's stdlib
3. It should handle basic server responses (HTTP 200 + 201 success status codes + 400 errors) by outputting error debug statements on the serial console
   • Note: the Ambi backend may not yes implement success response 201 after successfully responding to a POST request

Note: don't worry about implementing DNS lookups and using full on hostnames. For the PoC, we can just focus on using straight IP addresses.

Example ambi_mock_client output

Sending POST request to http://localhost:4000/api/readings/add as JSON: 
{"temperature":"16.7","humidity":"43.1","pressure":"1086","dust_concentration":"13","air_purity":"Dangerous Pollution"}
Response: Ok(
    Response {
        url: Url {
            scheme: "http",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: Some(
                Domain(
                    "localhost",
                ),
            ),
            port: Some(
                4000,
            ),
            path: "/api/readings/add",
            query: None,
            fragment: None,
        },
        status: 200,
        headers: {
            "cache-control": "max-age=0, private, must-revalidate",
            "content-length": "60",
            "content-type": "application/json; charset=utf-8",
            "date": "Wed, 23 Feb 2022 17:50:37 GMT",
            "server": "Cowboy",
            "x-request-id": "FtZ7n0Eot7jp2Q0AAV8n",
        },
    },
)

Tests

At this time, don't worry about writing unit/integration tests unless it will aid you in completing this work. We'll more intentionally focus on test writing in our next phase when we work to implement a mature ESP32 WiFi Rust crate.