Add Bearer Token authentication support

[Porrapat]

For now, we can add to use Bearer Token. We can do something like

use anyhow::Result;
use serde::Deserialize;
use serde_json::json;

const END_POINT: &str = "http://localhost:3000";

#[derive(Debug, Deserialize)]
struct LoginResponse {
    access_token: String,
}

#[tokio::main]
async fn main() -> Result<()> {
    let hc = httpc_test::new_client(END_POINT)?;

    let result = hc
        .do_post(
            "/api/login",
            json!({
                "email": "admin@website.com",
                "password": "password"
            }),
        )
        .await?;

    let login: LoginResponse = result.json_body_as()?;

    let access_token = login.access_token;
    println!("token = {}", access_token);

    let hc2 = httpc_test::new_client(END_POINT)?;
    let hcc2 = hc2.bearer_auth(access_token.clone());
    hcc2.do_get(
            "/api/dashboard",
        )
        .await?
        .print()
        .await?;

    hcc2.do_put(
            "/api/rename-something",
            json!({
                "title": "New Name",
            })
        )
        .await?
        .print()
        .await?;

    hcc2.do_post(
        "/api/logout",
        json!({})
    )
    .await?
    .print()
    .await?;

    Ok(())
}

Just the idea. I make this to use for myself.
Thank you for your wonderful open source software.